unexpected deepObject encoding of nil map

[SKalt]

I'm trying to use the zero value of a map as a tag-map query parameter type. This is producing an unexpected encoding, tags[]=null -- if there aren't any tags in the tag-map, no tags[] query parameters should be produced. Here's a reproduction case:

var nilTags map[string]string
result, _ := runtime.StyleParamWithOptions(
	"deepObject", true, "tags", nilTags,
	runtime.StyleParamOptions{ParamLocation: runtime.ParamLocationQuery},
)
fmt.Println("unexpected", result) // "tags[]=null"

(https://go.dev/play/p/Xa-sVpopeE_K)

This behavior is due to the json-marshalling-and-unmarshalling step in deepobject.go's MarshalDeepObject function, which obscures that the input is a nil map, not another type of nil.