NPE in AnnotationFields when entity extends a generic @MappedSuperclass more than one level deep

[dragkes]

Bug

A NullPointerException occurs at startup when an @Entity class extends a generic @MappedSuperclass through two or more levels of inheritance (e.g. Concrete extends Middle<Long> / Middle<T> extends Base<T>).

Stack trace

Caused by: java.lang.NullPointerException: Cannot invoke "java.lang.Class.isEnum()"
    because the return value of "io.ebeaninternal.server.deploy.meta.DeployBeanProperty.getPropertyType()" is null
    at io.ebeaninternal.server.deploy.parse.AnnotationFields.readField(AnnotationFields.java:121)
    at io.ebeaninternal.server.deploy.parse.AnnotationFields.parse(AnnotationFields.java:62)
    at io.ebeaninternal.server.deploy.parse.ReadAnnotations.readInitial(ReadAnnotations.java:29)

Reproducer

@MappedSuperclass
public abstract class GenericBaseModel<T> extends Model {
    @Id T id;
    // ...
}

@MappedSuperclass
public abstract class GenericMiddleModel<T> extends GenericBaseModel<T> {
    // intermediate layer
}

@Entity
@Table(name = "middle_product")
public class ProductWithGenericMiddle extends GenericMiddleModel<Long> {
    String name;
}

Ebean fails to start with the NPE above. The single-level case (Concrete extends GenericBaseModel<Long> directly) works correctly.

Root cause

Introduced in ebc90e0. DeployCreateProperties.mapGenerics(Class) built the TypeVariable → Class map by reading only the direct generic superclass of each class as the recursion walked up the hierarchy. For a chain like:

ProductWithGenericMiddle  extends  GenericMiddleModel<Long>
GenericMiddleModel<T>     extends  GenericBaseModel<T>
GenericBaseModel<T>       { @Id T id; }

When the recursion reached GenericBaseModel, it called mapGenerics(GenericMiddleModel). GenericMiddleModel.getGenericSuperclass() is GenericBaseModel<T> - where T is still an unresolved TypeVariable. resolveToClass(TypeVariable) returned null, so the map was empty. genericTypeMap.get(id.getGenericType()) then returned null, leaving propertyType = null. This null was stored in the DeployBeanProperty and caused the NPE in AnnotationFields.

Fix

Build the full type-variable map once for the concrete bean type using TypeResolver.getTypeVariableMap, which walks the entire superclass/interface hierarchy and composes TypeVariable bindings transitively (Middle.T → Long then Base.T → resolve(Middle.T) → Long). The same map is reused at every level of the recursive createProperties walk, so any TypeVariable at any depth in the hierarchy resolves correctly.

Additionally:

• The map type is widened from Map<TypeVariable<?>, Class<?>> to Map<TypeVariable<?>, Type> so intermediate ParameterizedType values (e.g. List<T>) are preserved and resolved transitively rather than being discarded.
• A null-safety fallback (propertyType = field.getType() when resolution yields null) prevents the NPE even for unresolvable type variables.
• Type-resolution helpers (resolveType, resolveToClass, resolveCollectionTarget) are consolidated in TypeReflectHelper for reuse.