diff --git a/client/base/src/test/java/org/a2aproject/sdk/client/ClientBuilderTest.java b/client/base/src/test/java/org/a2aproject/sdk/client/ClientBuilderTest.java
index 8df595122..3f1c120cc 100644
--- a/client/base/src/test/java/org/a2aproject/sdk/client/ClientBuilderTest.java
+++ b/client/base/src/test/java/org/a2aproject/sdk/client/ClientBuilderTest.java
@@ -163,13 +163,13 @@ public void shouldSelectCorrectInterfaceWithClientPreference() throws A2AClientE
     }
 
     @Test
-    public void shouldPreserveEmptyTenant() throws A2AClientException {
+    public void shouldHaveNullTenantWhenNotSet() throws A2AClientException {
         ClientBuilder builder = Client
                 .builder(card)
                 .withTransport(JSONRPCTransport.class, new JSONRPCTransportConfigBuilder());
 
         AgentInterface selectedInterface = builder.findBestClientTransport();
 
-        Assertions.assertEquals("", selectedInterface.tenant());
+        Assertions.assertNull(selectedInterface.tenant());
     }
 }
diff --git a/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/AgentInterfaceMapper.java b/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/AgentInterfaceMapper.java
index 81b476088..d7b51224f 100644
--- a/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/AgentInterfaceMapper.java
+++ b/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/AgentInterfaceMapper.java
@@ -8,12 +8,15 @@
  * Mapper between {@link org.a2aproject.sdk.spec.AgentInterface} and {@link org.a2aproject.sdk.grpc.AgentInterface}.
  */
 @Mapper(config = A2AProtoMapperConfig.class,
-        collectionMappingStrategy = CollectionMappingStrategy.ADDER_PREFERRED)
+        collectionMappingStrategy = CollectionMappingStrategy.ADDER_PREFERRED,
+        uses = A2ACommonFieldMapper.class)
 public interface AgentInterfaceMapper {
 
     AgentInterfaceMapper INSTANCE = A2AMappers.getMapper(AgentInterfaceMapper.class);
 
+    @Mapping(target = "tenant", source = "tenant", conditionExpression = "java(domain.tenant() != null)")
     org.a2aproject.sdk.grpc.AgentInterface toProto(org.a2aproject.sdk.spec.AgentInterface domain);
 
+    @Mapping(target = "tenant", source = "tenant", qualifiedByName = "emptyToNull")
     org.a2aproject.sdk.spec.AgentInterface fromProto(org.a2aproject.sdk.grpc.AgentInterface proto);
 }
diff --git a/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/DeleteTaskPushNotificationConfigParamsMapper.java b/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/DeleteTaskPushNotificationConfigParamsMapper.java
index 18fc3ae9d..a464dfab2 100644
--- a/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/DeleteTaskPushNotificationConfigParamsMapper.java
+++ b/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/DeleteTaskPushNotificationConfigParamsMapper.java
@@ -9,7 +9,7 @@
 /**
  * Mapper between {@link org.a2aproject.sdk.grpc.DeleteTaskPushNotificationConfigRequest} and {@link org.a2aproject.sdk.spec.DeleteTaskPushNotificationConfigParams}.
  */
-@Mapper(config = A2AProtoMapperConfig.class)
+@Mapper(config = A2AProtoMapperConfig.class, uses = A2ACommonFieldMapper.class)
 public interface DeleteTaskPushNotificationConfigParamsMapper {
 
     DeleteTaskPushNotificationConfigParamsMapper INSTANCE = A2AMappers.getMapper(DeleteTaskPushNotificationConfigParamsMapper.class);
@@ -20,7 +20,7 @@ public interface DeleteTaskPushNotificationConfigParamsMapper {
     @BeanMapping(builder = @Builder(buildMethod = "build"))
     @Mapping(target = "taskId", source = "taskId")
     @Mapping(target = "id", source = "id")
-    @Mapping(target = "tenant", source = "tenant")
+    @Mapping(target = "tenant", source = "tenant", qualifiedByName = "emptyToNull")
     DeleteTaskPushNotificationConfigParams fromProto(org.a2aproject.sdk.grpc.DeleteTaskPushNotificationConfigRequest proto);
 
     /**
@@ -28,6 +28,6 @@ public interface DeleteTaskPushNotificationConfigParamsMapper {
      */
     @Mapping(target = "taskId", source = "taskId")
     @Mapping(target = "id", source = "id")
-    @Mapping(target = "tenant", source = "tenant")
+    @Mapping(target = "tenant", source = "tenant", conditionExpression = "java(domain.tenant() != null)")
     org.a2aproject.sdk.grpc.DeleteTaskPushNotificationConfigRequest toProto(DeleteTaskPushNotificationConfigParams domain);
 }
diff --git a/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/GetTaskPushNotificationConfigParamsMapper.java b/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/GetTaskPushNotificationConfigParamsMapper.java
index 9febadf56..e277b7ce0 100644
--- a/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/GetTaskPushNotificationConfigParamsMapper.java
+++ b/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/GetTaskPushNotificationConfigParamsMapper.java
@@ -9,7 +9,7 @@
 /**
  * Mapper between {@link org.a2aproject.sdk.grpc.GetTaskPushNotificationConfigRequest} and {@link org.a2aproject.sdk.spec.GetTaskPushNotificationConfigParams}.
  */
-@Mapper(config = A2AProtoMapperConfig.class)
+@Mapper(config = A2AProtoMapperConfig.class, uses = A2ACommonFieldMapper.class)
 public interface GetTaskPushNotificationConfigParamsMapper {
 
     GetTaskPushNotificationConfigParamsMapper INSTANCE = A2AMappers.getMapper(GetTaskPushNotificationConfigParamsMapper.class);
@@ -20,7 +20,7 @@ public interface GetTaskPushNotificationConfigParamsMapper {
     @BeanMapping(builder = @Builder(buildMethod = "build"))
     @Mapping(target = "taskId", source = "taskId")
     @Mapping(target = "id", source = "id")
-    @Mapping(target = "tenant", source = "tenant")
+    @Mapping(target = "tenant", source = "tenant", qualifiedByName = "emptyToNull")
     GetTaskPushNotificationConfigParams fromProto(org.a2aproject.sdk.grpc.GetTaskPushNotificationConfigRequest proto);
 
     /**
@@ -28,6 +28,6 @@ public interface GetTaskPushNotificationConfigParamsMapper {
      */
     @Mapping(target = "taskId", source = "taskId")
     @Mapping(target = "id", source = "id", conditionExpression = "java(domain.id() != null)")
-    @Mapping(target = "tenant", source = "tenant")
+    @Mapping(target = "tenant", source = "tenant", conditionExpression = "java(domain.tenant() != null)")
     org.a2aproject.sdk.grpc.GetTaskPushNotificationConfigRequest toProto(GetTaskPushNotificationConfigParams domain);
 }
diff --git a/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/ListTaskPushNotificationConfigsParamsMapper.java b/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/ListTaskPushNotificationConfigsParamsMapper.java
index 635600bf2..c69fa1925 100644
--- a/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/ListTaskPushNotificationConfigsParamsMapper.java
+++ b/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/ListTaskPushNotificationConfigsParamsMapper.java
@@ -9,7 +9,7 @@
 /**
  * Mapper between {@link org.a2aproject.sdk.grpc.ListTaskPushNotificationConfigsRequest} and {@link org.a2aproject.sdk.spec.ListTaskPushNotificationConfigsParams}.
  */
-@Mapper(config = A2AProtoMapperConfig.class)
+@Mapper(config = A2AProtoMapperConfig.class, uses = A2ACommonFieldMapper.class)
 public interface ListTaskPushNotificationConfigsParamsMapper {
 
     ListTaskPushNotificationConfigsParamsMapper INSTANCE = A2AMappers.getMapper(ListTaskPushNotificationConfigsParamsMapper.class);
@@ -19,13 +19,13 @@ public interface ListTaskPushNotificationConfigsParamsMapper {
      */
     @BeanMapping(builder = @Builder(buildMethod = "build"))
     @Mapping(target = "id", source = "taskId")
-    @Mapping(target = "tenant", source = "tenant")
+    @Mapping(target = "tenant", source = "tenant", qualifiedByName = "emptyToNull")
     ListTaskPushNotificationConfigsParams fromProto(org.a2aproject.sdk.grpc.ListTaskPushNotificationConfigsRequest proto);
 
     /**
      * Converts domain ListTaskPushNotificationConfigsParams to proto ListTaskPushNotificationConfigsRequest.
      */
     @Mapping(target = "taskId", source = "id")
-    @Mapping(target = "tenant", source = "tenant")
+    @Mapping(target = "tenant", source = "tenant", conditionExpression = "java(domain.tenant() != null)")
     org.a2aproject.sdk.grpc.ListTaskPushNotificationConfigsRequest toProto(ListTaskPushNotificationConfigsParams domain);
 }
diff --git a/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/MessageSendParamsMapper.java b/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/MessageSendParamsMapper.java
index 78bec7580..0325ca527 100644
--- a/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/MessageSendParamsMapper.java
+++ b/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/MessageSendParamsMapper.java
@@ -22,6 +22,7 @@ public interface MessageSendParamsMapper {
      */
     @Mapping(target = "configuration", source = "configuration", conditionExpression = "java(domain.configuration() != null)")
     @Mapping(target = "metadata", source = "metadata", qualifiedByName = "metadataToProto")
+    @Mapping(target = "tenant", source = "tenant", conditionExpression = "java(domain.tenant() != null)")
     org.a2aproject.sdk.grpc.SendMessageRequest toProto(MessageSendParams domain);
 
     /**
@@ -31,5 +32,6 @@ public interface MessageSendParamsMapper {
      */
     @BeanMapping(builder = @Builder(buildMethod = "build"))
     @Mapping(target = "metadata", source = "metadata", qualifiedByName = "metadataFromProto")
+    @Mapping(target = "tenant", source = "tenant", qualifiedByName = "emptyToNull")
     MessageSendParams fromProto(org.a2aproject.sdk.grpc.SendMessageRequest proto);
 }
diff --git a/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/TaskIdParamsMapper.java b/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/TaskIdParamsMapper.java
index b42d9379a..d6f3a913d 100644
--- a/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/TaskIdParamsMapper.java
+++ b/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/TaskIdParamsMapper.java
@@ -24,6 +24,7 @@ public interface TaskIdParamsMapper {
     @BeanMapping(builder = @Builder(buildMethod = "build"))
     @Mapping(target = "id", source = "id")
     @Mapping(target = "metadata", source = "metadata", qualifiedByName = "metadataFromProto")
+    @Mapping(target = "tenant", source = "tenant", qualifiedByName = "emptyToNull")
     CancelTaskParams fromProtoCancelTaskRequest(org.a2aproject.sdk.grpc.CancelTaskRequest proto);
     
      /**
@@ -33,6 +34,7 @@ public interface TaskIdParamsMapper {
     @BeanMapping(builder = @Builder(buildMethod = "build"))
     @Mapping(target = "id", source = "id")
     @Mapping(target = "metadata", source = "metadata", qualifiedByName = "metadataToProto")
+    @Mapping(target = "tenant", source = "tenant", conditionExpression = "java(domain.tenant() != null)")
     org.a2aproject.sdk.grpc.CancelTaskRequest toProtoCancelTaskRequest(CancelTaskParams domain);
 
 
@@ -42,7 +44,7 @@ public interface TaskIdParamsMapper {
      */
     @BeanMapping(builder = @Builder(buildMethod = "build"))
     @Mapping(target = "id", source = "id")
-    @Mapping(target = "tenant", source = "tenant")
+    @Mapping(target = "tenant", source = "tenant", qualifiedByName = "emptyToNull")
     TaskIdParams fromProtoSubscribeToTaskRequest(org.a2aproject.sdk.grpc.SubscribeToTaskRequest proto);
 
     /**
@@ -51,5 +53,6 @@ public interface TaskIdParamsMapper {
      */
     @BeanMapping(builder = @Builder(buildMethod = "build"))
     @Mapping(target = "id", source = "id")
+    @Mapping(target = "tenant", source = "tenant", conditionExpression = "java(domain.tenant() != null)")
     org.a2aproject.sdk.grpc.SubscribeToTaskRequest toProtoSubscribeToTaskRequest(TaskIdParams domain);
 }
diff --git a/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/TaskQueryParamsMapper.java b/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/TaskQueryParamsMapper.java
index fe5916a47..d95147b75 100644
--- a/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/TaskQueryParamsMapper.java
+++ b/spec-grpc/src/main/java/org/a2aproject/sdk/grpc/mapper/TaskQueryParamsMapper.java
@@ -11,7 +11,7 @@
  * <p>
  * Extracts task ID from resource name format "tasks/{id}" using {@link ResourceNameParser}.
  */
-@Mapper(config = A2AProtoMapperConfig.class)
+@Mapper(config = A2AProtoMapperConfig.class, uses = A2ACommonFieldMapper.class)
 public interface TaskQueryParamsMapper {
 
     TaskQueryParamsMapper INSTANCE = A2AMappers.getMapper(TaskQueryParamsMapper.class);
@@ -28,6 +28,6 @@ public interface TaskQueryParamsMapper {
     @BeanMapping(builder = @Builder(buildMethod = "build"))
     @Mapping(target = "id", source = "id")
     @Mapping(target = "historyLength", source = "historyLength")
-    @Mapping(target = "tenant", source = "tenant")
+    @Mapping(target = "tenant", source = "tenant", conditionExpression = "java(domain.tenant() != null)")
     org.a2aproject.sdk.grpc.GetTaskRequest toProto(TaskQueryParams domain);
 }
diff --git a/spec/src/main/java/org/a2aproject/sdk/spec/AgentInterface.java b/spec/src/main/java/org/a2aproject/sdk/spec/AgentInterface.java
index c14147eee..3ad2d4717 100644
--- a/spec/src/main/java/org/a2aproject/sdk/spec/AgentInterface.java
+++ b/spec/src/main/java/org/a2aproject/sdk/spec/AgentInterface.java
@@ -1,6 +1,7 @@
 package org.a2aproject.sdk.spec;
 
 import org.a2aproject.sdk.util.Assert;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Declares a combination of a target URL and protocol binding for accessing an agent.
@@ -19,13 +20,13 @@
  * @param protocolBinding the protocol binding supported at this URL (e.g., "JSONRPC", "GRPC", "HTTP+JSON") (required)
  * @param url the endpoint URL where this interface is available; must be a valid absolute HTTPS URL in production
  * (required)
- * @param tenant the tenant to be set in the request when calling the agent.
+ * @param tenant optional tenant to be set in the request when calling the agent.
  * @param protocolVersion the version of the A2A protocol this interface exposes (e.g., "1.0", "0.3") (required)
  * @see AgentCard
  * @see TransportProtocol
  * @see <a href="https://a2a-protocol.org/latest/">A2A Protocol Specification</a>
  */
-public record AgentInterface(String protocolBinding, String url, String tenant, String protocolVersion) {
+public record AgentInterface(String protocolBinding, String url, @Nullable String tenant, String protocolVersion) {
 
     /** The default A2A Protocol version used when not explicitly specified. */
     public static final String CURRENT_PROTOCOL_VERSION = "1.0";
@@ -42,7 +43,6 @@ public record AgentInterface(String protocolBinding, String url, String tenant,
     public AgentInterface   {
         Assert.checkNotNullParam("protocolBinding", protocolBinding);
         Assert.checkNotNullParam("url", url);
-        Assert.checkNotNullParam("tenant", tenant);
 
         if (protocolVersion == null || protocolVersion.isEmpty()) {
             protocolVersion = CURRENT_PROTOCOL_VERSION;
@@ -67,6 +67,6 @@ public AgentInterface(String protocolBinding, String url, String tenant) {
      * @param url the endpoint URL (see class-level JavaDoc)
      */
     public AgentInterface(String protocolBinding, String url) {
-        this(protocolBinding, url, "", CURRENT_PROTOCOL_VERSION);
+        this(protocolBinding, url, null, CURRENT_PROTOCOL_VERSION);
     }
 }
diff --git a/spec/src/main/java/org/a2aproject/sdk/spec/CancelTaskParams.java b/spec/src/main/java/org/a2aproject/sdk/spec/CancelTaskParams.java
index d950f1793..e823af312 100644
--- a/spec/src/main/java/org/a2aproject/sdk/spec/CancelTaskParams.java
+++ b/spec/src/main/java/org/a2aproject/sdk/spec/CancelTaskParams.java
@@ -1,7 +1,6 @@
 package org.a2aproject.sdk.spec;
 
 import org.a2aproject.sdk.util.Assert;
-import org.a2aproject.sdk.util.Utils;
 import java.util.Collections;
 import java.util.Map;
 import org.jspecify.annotations.Nullable;
@@ -17,7 +16,7 @@
  * @param metadata optional arbitrary key-value metadata (e.g. cancellation reason)
  * @see <a href="https://a2a-protocol.org/latest/">A2A Protocol Specification</a>
  */
-public record CancelTaskParams(String id, String tenant, Map<String, Object> metadata) {
+public record CancelTaskParams(String id, @Nullable String tenant, Map<String, Object> metadata) {
 
     /**
      * Compact constructor for validation.
@@ -28,7 +27,6 @@ public record CancelTaskParams(String id, String tenant, Map<String, Object> met
      */
     public CancelTaskParams {
         Assert.checkNotNullParam("id", id);
-        Assert.checkNotNullParam("tenant", tenant);
     }
 
     /**
@@ -37,7 +35,7 @@ public record CancelTaskParams(String id, String tenant, Map<String, Object> met
      * @param id the task identifier (required)
      */
     public CancelTaskParams(String id) {
-        this(id, "", Collections.emptyMap());
+        this(id, null, Collections.emptyMap());
     }
 
     /**
@@ -80,7 +78,7 @@ public Builder id(String id) {
          * @param tenant the tenant identifier
          * @return this builder for method chaining
          */
-        public Builder tenant(String tenant) {
+        public Builder tenant(@Nullable String tenant) {
             this.tenant = tenant;
             return this;
         }
@@ -105,7 +103,7 @@ public Builder metadata(Map<String, Object> metadata) {
         public CancelTaskParams build() {
             return new CancelTaskParams(
                 Assert.checkNotNullParam("id", id),
-                Utils.defaultIfNull(tenant,""),
+                tenant,
                 metadata
             );
         }
diff --git a/spec/src/main/java/org/a2aproject/sdk/spec/DeleteTaskPushNotificationConfigParams.java b/spec/src/main/java/org/a2aproject/sdk/spec/DeleteTaskPushNotificationConfigParams.java
index 96728e8fe..517cc7379 100644
--- a/spec/src/main/java/org/a2aproject/sdk/spec/DeleteTaskPushNotificationConfigParams.java
+++ b/spec/src/main/java/org/a2aproject/sdk/spec/DeleteTaskPushNotificationConfigParams.java
@@ -3,7 +3,6 @@
 
 
 import org.a2aproject.sdk.util.Assert;
-import org.a2aproject.sdk.util.Utils;
 import org.jspecify.annotations.Nullable;
 
 /**
@@ -17,7 +16,7 @@
  * @param tenant optional tenant, provided as a path parameter.
  * @see <a href="https://a2a-protocol.org/latest/">A2A Protocol Specification</a>
  */
-public record DeleteTaskPushNotificationConfigParams(String taskId, String id, String tenant) {
+public record DeleteTaskPushNotificationConfigParams(String taskId, String id, @Nullable String tenant) {
 
     /**
      * Compact constructor that validates required fields.
@@ -30,7 +29,6 @@ public record DeleteTaskPushNotificationConfigParams(String taskId, String id, S
     public DeleteTaskPushNotificationConfigParams {
         Assert.checkNotNullParam("taskId", taskId);
         Assert.checkNotNullParam("id", id);
-        Assert.checkNotNullParam("tenant", tenant);
     }
 
     /**
@@ -41,7 +39,7 @@ public record DeleteTaskPushNotificationConfigParams(String taskId, String id, S
      * @throws IllegalArgumentException if taskId or id is null
      */
     public DeleteTaskPushNotificationConfigParams(String taskId, String id) {
-        this(taskId, id, "");
+        this(taskId, id, null);
     }
 
     /**
@@ -97,7 +95,7 @@ public Builder id(String id) {
          * @param tenant arbitrary tenant (optional)
          * @return this builder for method chaining
          */
-        public Builder tenant(String tenant) {
+        public Builder tenant(@Nullable String tenant) {
             this.tenant = tenant;
             return this;
         }
@@ -112,7 +110,7 @@ public DeleteTaskPushNotificationConfigParams build() {
             return new DeleteTaskPushNotificationConfigParams(
                     Assert.checkNotNullParam("taskId", taskId),
                     Assert.checkNotNullParam("id", id),
-                    Utils.defaultIfNull(tenant,""));
+                    tenant);
         }
     }
 }
diff --git a/spec/src/main/java/org/a2aproject/sdk/spec/GetTaskPushNotificationConfigParams.java b/spec/src/main/java/org/a2aproject/sdk/spec/GetTaskPushNotificationConfigParams.java
index 0d2bfc453..d405c21c7 100644
--- a/spec/src/main/java/org/a2aproject/sdk/spec/GetTaskPushNotificationConfigParams.java
+++ b/spec/src/main/java/org/a2aproject/sdk/spec/GetTaskPushNotificationConfigParams.java
@@ -3,7 +3,6 @@
 
 
 import org.a2aproject.sdk.util.Assert;
-import org.a2aproject.sdk.util.Utils;
 import org.jspecify.annotations.Nullable;
 
 /**
@@ -18,7 +17,7 @@
  * @see TaskPushNotificationConfig for the returned configuration structure
  * @see <a href="https://a2a-protocol.org/latest/">A2A Protocol Specification</a>
  */
-public record GetTaskPushNotificationConfigParams(String taskId, String id, String tenant) {
+public record GetTaskPushNotificationConfigParams(String taskId, String id, @Nullable String tenant) {
 
     /**
      * Compact constructor that validates required fields.
@@ -31,7 +30,6 @@ public record GetTaskPushNotificationConfigParams(String taskId, String id, Stri
     public GetTaskPushNotificationConfigParams {
         Assert.checkNotNullParam("taskId", taskId);
         Assert.checkNotNullParam("id", id);
-        Assert.checkNotNullParam("tenant", tenant);
     }
 
     /**
@@ -41,7 +39,7 @@ public record GetTaskPushNotificationConfigParams(String taskId, String id, Stri
      * @param id optional configuration ID to retrieve
      */
     public GetTaskPushNotificationConfigParams(String taskId, String id) {
-        this(taskId, id, "");
+        this(taskId, id, null);
     }
 
     /**
@@ -95,7 +93,7 @@ public Builder id(String id) {
          * @param tenant the tenant
          * @return this builder for method chaining
          */
-        public Builder tenant(String tenant) {
+        public Builder tenant(@Nullable String tenant) {
             this.tenant = tenant;
             return this;
         }
@@ -109,7 +107,7 @@ public GetTaskPushNotificationConfigParams build() {
             return new GetTaskPushNotificationConfigParams(
                     Assert.checkNotNullParam("taskId", taskId),
                     Assert.checkNotNullParam("id", id),
-                    Utils.defaultIfNull(tenant,""));
+                    tenant);
         }
     }
 }
diff --git a/spec/src/main/java/org/a2aproject/sdk/spec/ListTaskPushNotificationConfigsParams.java b/spec/src/main/java/org/a2aproject/sdk/spec/ListTaskPushNotificationConfigsParams.java
index 1e2389b16..36d0f58fb 100644
--- a/spec/src/main/java/org/a2aproject/sdk/spec/ListTaskPushNotificationConfigsParams.java
+++ b/spec/src/main/java/org/a2aproject/sdk/spec/ListTaskPushNotificationConfigsParams.java
@@ -1,7 +1,6 @@
 package org.a2aproject.sdk.spec;
 
 import org.a2aproject.sdk.util.Assert;
-import org.a2aproject.sdk.util.Utils;
 import org.jspecify.annotations.Nullable;
 
 /**
@@ -17,7 +16,7 @@
  * @see TaskPushNotificationConfig for the configuration structure
  * @see <a href="https://a2a-protocol.org/latest/">A2A Protocol Specification</a>
  */
-public record ListTaskPushNotificationConfigsParams(String id, int pageSize, String pageToken, String tenant) {
+public record ListTaskPushNotificationConfigsParams(String id, int pageSize, String pageToken, @Nullable String tenant) {
 
     /**
      * Compact constructor for validation.
@@ -30,7 +29,6 @@ public record ListTaskPushNotificationConfigsParams(String id, int pageSize, Str
      */
     public ListTaskPushNotificationConfigsParams {
         Assert.checkNotNullParam("id", id);
-        Assert.checkNotNullParam("tenant", tenant);
     }
 
     /**
@@ -39,7 +37,7 @@ public record ListTaskPushNotificationConfigsParams(String id, int pageSize, Str
      * @param id the task identifier (required)
      */
     public ListTaskPushNotificationConfigsParams(String id) {
-        this(id, 0, "", "");
+        this(id, 0, "", null);
     }
 
     /**
@@ -117,7 +115,7 @@ public Builder pageToken(String pageToken) {
          * @param tenant the tenant identifier
          * @return this builder for method chaining
          */
-        public Builder tenant(String tenant) {
+        public Builder tenant(@Nullable String tenant) {
             this.tenant = tenant;
             return this;
         }
@@ -133,7 +131,7 @@ public ListTaskPushNotificationConfigsParams build() {
                 Assert.checkNotNullParam("id", id),
                 pageSize != null ? pageSize : 0,
                 pageToken != null ? pageToken : "",
-                Utils.defaultIfNull(tenant,"")
+                tenant
             );
         }
     }
diff --git a/spec/src/main/java/org/a2aproject/sdk/spec/ListTasksParams.java b/spec/src/main/java/org/a2aproject/sdk/spec/ListTasksParams.java
index ee4387d26..20d3d70b6 100644
--- a/spec/src/main/java/org/a2aproject/sdk/spec/ListTasksParams.java
+++ b/spec/src/main/java/org/a2aproject/sdk/spec/ListTasksParams.java
@@ -25,7 +25,7 @@ public record ListTasksParams(
         @Nullable Integer historyLength,
         @Nullable Instant statusTimestampAfter,
         @Nullable Boolean includeArtifacts,
-        String tenant
+        @Nullable String tenant
 ) {
     private static final int MIN_PAGE_SIZE = 1;
     private static final int MAX_PAGE_SIZE = 100;
@@ -42,10 +42,9 @@ public record ListTasksParams(
      * @param statusTimestampAfter filter by status timestamp
      * @param includeArtifacts whether to include artifacts
      * @param tenant the tenant identifier
-     * @throws InvalidParamsError if tenant is null or if pageSize or historyLength are out of valid range
+     * @throws InvalidParamsError if pageSize or historyLength are out of valid range
      */
     public ListTasksParams {
-        Assert.checkNotNullParam("tenant", tenant);
         // Validate pageSize (1-100)
         if (pageSize != null && (pageSize < MIN_PAGE_SIZE || pageSize > MAX_PAGE_SIZE)) {
             throw new InvalidParamsError(null,
@@ -62,7 +61,7 @@ public record ListTasksParams(
      * Default constructor for listing all tasks.
      */
     public ListTasksParams() {
-        this(null, null, null, null, null, null, null, "");
+        this(null, null, null, null, null, null, null, null);
     }
 
     /**
@@ -72,7 +71,7 @@ public ListTasksParams() {
      * @param pageToken Token for pagination
      */
     public ListTasksParams(Integer pageSize, String pageToken) {
-        this(null, null, pageSize, pageToken, null, null, null, "");
+        this(null, null, pageSize, pageToken, null, null, null, null);
     }
 
     /**
@@ -215,7 +214,7 @@ public Builder includeArtifacts(Boolean includeArtifacts) {
          * @param tenant the tenant
          * @return this builder for method chaining
          */
-        public Builder tenant(String tenant) {
+        public Builder tenant(@Nullable String tenant) {
             this.tenant = tenant;
             return this;
         }
@@ -227,7 +226,7 @@ public Builder tenant(String tenant) {
          */
         public ListTasksParams build() {
             return new ListTasksParams(contextId, status, pageSize, pageToken, historyLength,
-                    statusTimestampAfter, includeArtifacts, tenant == null ? "" : tenant);
+                    statusTimestampAfter, includeArtifacts, tenant);
         }
     }
 }
diff --git a/spec/src/main/java/org/a2aproject/sdk/spec/MessageSendParams.java b/spec/src/main/java/org/a2aproject/sdk/spec/MessageSendParams.java
index bb0156d99..0f4bafe5f 100644
--- a/spec/src/main/java/org/a2aproject/sdk/spec/MessageSendParams.java
+++ b/spec/src/main/java/org/a2aproject/sdk/spec/MessageSendParams.java
@@ -22,7 +22,7 @@
  * @see <a href="https://a2a-protocol.org/latest/">A2A Protocol Specification</a>
  */
 public record MessageSendParams(Message message, @Nullable MessageSendConfiguration configuration,
-                                @Nullable Map<String, Object> metadata, String tenant) {
+                                @Nullable Map<String, Object> metadata, @Nullable String tenant) {
 
     /**
      * Compact constructor for validation.
@@ -35,7 +35,6 @@ public record MessageSendParams(Message message, @Nullable MessageSendConfigurat
      */
     public MessageSendParams {
         Assert.checkNotNullParam("message", message);
-        Assert.checkNotNullParam("tenant", tenant);
     }
 
     /**
@@ -46,7 +45,7 @@ public record MessageSendParams(Message message, @Nullable MessageSendConfigurat
      * @param metadata optional metadata
      */
      public MessageSendParams(Message message, @Nullable MessageSendConfiguration configuration, @Nullable Map<String, Object> metadata) {
-        this(message, configuration, metadata, "");
+        this(message, configuration, metadata, null);
     }
 
     /**
@@ -115,7 +114,7 @@ public Builder metadata(@Nullable Map<String, Object> metadata) {
          * @param tenant arbitrary key-value metadata
          * @return this builder
          */
-        public Builder tenant(String tenant) {
+        public Builder tenant(@Nullable String tenant) {
             this.tenant = tenant;
             return this;
         }
@@ -131,7 +130,7 @@ public MessageSendParams build() {
                     Assert.checkNotNullParam("message", message),
                     configuration,
                     metadata,
-                    tenant == null ? "" : tenant);
+                    tenant);
         }
     }
 }
diff --git a/spec/src/main/java/org/a2aproject/sdk/spec/TaskIdParams.java b/spec/src/main/java/org/a2aproject/sdk/spec/TaskIdParams.java
index 1bef6d7a9..e92ce222a 100644
--- a/spec/src/main/java/org/a2aproject/sdk/spec/TaskIdParams.java
+++ b/spec/src/main/java/org/a2aproject/sdk/spec/TaskIdParams.java
@@ -1,7 +1,6 @@
 package org.a2aproject.sdk.spec;
 
 import org.a2aproject.sdk.util.Assert;
-import org.a2aproject.sdk.util.Utils;
 import org.jspecify.annotations.Nullable;
 
 /**
@@ -14,7 +13,7 @@
  * @param tenant optional tenant, provided as a path parameter.
  * @see <a href="https://a2a-protocol.org/latest/">A2A Protocol Specification</a>
  */
-public record TaskIdParams(String id, String tenant) {
+public record TaskIdParams(String id, @Nullable String tenant) {
 
     /**
      * Compact constructor for validation.
@@ -25,7 +24,6 @@ public record TaskIdParams(String id, String tenant) {
      */
     public TaskIdParams  {
         Assert.checkNotNullParam("id", id);
-        Assert.checkNotNullParam("tenant", tenant);
     }
 
     /**
@@ -34,7 +32,7 @@ public record TaskIdParams(String id, String tenant) {
      * @param id the task identifier (required)
      */
     public TaskIdParams(String id) {
-        this(id, "");
+        this(id, null);
     }
 
     /**
@@ -76,7 +74,7 @@ public Builder id(String id) {
          * @param tenant the tenant identifier
          * @return this builder for method chaining
          */
-        public Builder tenant(String tenant) {
+        public Builder tenant(@Nullable String tenant) {
             this.tenant = tenant;
             return this;
         }
@@ -91,7 +89,7 @@ public Builder tenant(String tenant) {
         public TaskIdParams build() {
             return new TaskIdParams(
                 Assert.checkNotNullParam("id", id),
-                Utils.defaultIfNull(tenant,"")
+                tenant
             );
         }
     }
diff --git a/spec/src/main/java/org/a2aproject/sdk/spec/TaskQueryParams.java b/spec/src/main/java/org/a2aproject/sdk/spec/TaskQueryParams.java
index 281357929..56c636371 100644
--- a/spec/src/main/java/org/a2aproject/sdk/spec/TaskQueryParams.java
+++ b/spec/src/main/java/org/a2aproject/sdk/spec/TaskQueryParams.java
@@ -1,7 +1,6 @@
 package org.a2aproject.sdk.spec;
 
 import org.a2aproject.sdk.util.Assert;
-import org.a2aproject.sdk.util.Utils;
 import org.jspecify.annotations.Nullable;
 
 /**
@@ -11,7 +10,7 @@
  * @param historyLength the maximum number of items of history for the task to include in the response
  * @param tenant optional tenant, provided as a path parameter.
  */
-public record TaskQueryParams(String id, @Nullable Integer historyLength, String tenant) {
+public record TaskQueryParams(String id, @Nullable Integer historyLength, @Nullable String tenant) {
 
     /**
      * Compact constructor for validation.
@@ -24,7 +23,6 @@ public record TaskQueryParams(String id, @Nullable Integer historyLength, String
      */
     public TaskQueryParams {
         Assert.checkNotNullParam("id", id);
-        Assert.checkNotNullParam("tenant", tenant);
         if (historyLength != null && historyLength < 0) {
             throw new IllegalArgumentException("Invalid history length");
         }
@@ -37,7 +35,7 @@ public record TaskQueryParams(String id, @Nullable Integer historyLength, String
      * @param historyLength maximum number of history items to include (optional)
      */
     public TaskQueryParams(String id, @Nullable Integer historyLength) {
-        this(id, historyLength, "");
+        this(id, historyLength, null);
     }
 
     /**
@@ -46,7 +44,7 @@ public TaskQueryParams(String id, @Nullable Integer historyLength) {
      * @param id the task identifier (required)
      */
     public TaskQueryParams(String id) {
-        this(id, null, "");
+        this(id, null, null);
     }
 
     /**
@@ -100,7 +98,7 @@ public Builder historyLength(Integer historyLength) {
          * @param tenant the tenant identifier
          * @return this builder for method chaining
          */
-        public Builder tenant(String tenant) {
+        public Builder tenant(@Nullable String tenant) {
             this.tenant = tenant;
             return this;
         }
@@ -115,7 +113,7 @@ public TaskQueryParams build() {
             return new TaskQueryParams(
                 Assert.checkNotNullParam("id", id),
                 historyLength,
-                Utils.defaultIfNull(tenant,"")
+                tenant
             );
         }
     }
diff --git a/spec/src/main/java/org/a2aproject/sdk/util/Utils.java b/spec/src/main/java/org/a2aproject/sdk/util/Utils.java
index ce50dc30f..d605f6f14 100644
--- a/spec/src/main/java/org/a2aproject/sdk/util/Utils.java
+++ b/spec/src/main/java/org/a2aproject/sdk/util/Utils.java
@@ -189,7 +189,8 @@ public static void validateAbsoluteUrl(String url) throws URISyntaxException {
     /**
      * Normalizes {@code baseUrl} and {@code cardPath} and concatenates them into a full card URL.
      *
-     * <p>Strips any trailing slash from {@code baseUrl} and ensures {@code cardPath} starts with
+     * <p>
+     * Strips any trailing slash from {@code baseUrl} and ensures {@code cardPath} starts with
      * a leading slash before concatenating, so both {@code http://host/base/} and
      * {@code http://host/base} produce the same result.
      *
@@ -206,7 +207,8 @@ public static String buildCardUrl(String baseUrl, String cardPath) {
      * Strips any trailing slash and the standard well-known suffix from {@code baseUrl} so that
      * {@link #buildCardUrl} can append the desired path without doubling it.
      *
-     * <p>Only {@link #DEFAULT_AGENT_CARD_PATH} is stripped; custom paths are never inferred
+     * <p>
+     * Only {@link #DEFAULT_AGENT_CARD_PATH} is stripped; custom paths are never inferred
      * from the URL structure.
      *
      * @param baseUrl the URL to strip
@@ -222,7 +224,8 @@ public static String stripWellKnownSuffix(String baseUrl) {
     /**
      * Builds a base URL by combining a raw base URL string with an optional tenant path.
      *
-     * <p>Normalizes trailing slashes on the base URL and validates/normalizes the tenant path.
+     * <p>
+     * Normalizes trailing slashes on the base URL and validates/normalizes the tenant path.
      *
      * @param baseUrl the base URL string, must not be null
      * @param tenant the tenant path override, may be null for no tenant
@@ -299,17 +302,18 @@ private static void validateTenant(String tenant) {
      * <p>
      * If the provided {@code tenant} parameter is null or blank, the {@code agentTenant} is returned instead.
      *
-     * @param agentTenant the default tenant from the agent card, must not be null
+     * @param agentTenant the default tenant from the agent card, may be null or blank
      * @param tenant the tenant override from the request, may be null or blank
      * @return the normalized tenant path
      * @throws IllegalArgumentException if the tenant is invalid or unsafe
      */
-    private static String extractTenant(String agentTenant, @Nullable String tenant) {
-        checkNotNullParam("agentTenant", agentTenant);
-
+    private static String extractTenant(@Nullable String agentTenant, @Nullable String tenant) {
         String tenantPath = tenant;
         if (tenantPath == null || tenantPath.isBlank()) {
-            return agentTenant;
+            tenantPath = agentTenant;
+        }
+        if (tenantPath == null || tenantPath.isBlank()) {
+            return "";
         }
 
         // Normalize slashes