Java SDK allows empty subject during deserialization

[pnt]

Hi,

Specification says that "subject" is optional but if present, must be non-empty.

Doing a simple test with structured or binary event delivery shows that this is not validated by the standard deserializers - the screenshot below shows how a test expecting a 400 Bad Request actually passes with 200 OK.

[pierDipi]

Would you be interested in contributing?

We need to update the 2 builders with the subject validation:

• sdk-java/core/src/main/java/io/cloudevents/core/v03/CloudEventBuilder.java

  Lines 117 to 133 in a3decf7

  	public CloudEventV03 build() {
  	if (id == null) {
  	throw createMissingAttributeException("id");
  	}
  	if (source == null) {
  	throw createMissingAttributeException("source");
  	}
  	if (type == null) {
  	throw createMissingAttributeException("type");
  	}
  	CloudEventV03 cloudEvent = new CloudEventV03(id, source, type, time, schemaurl, datacontenttype, subject, this.data, this.extensions);
  	final CloudEventValidatorProvider validator = CloudEventValidatorProvider.getInstance();
  	validator.validate(cloudEvent);
  	return cloudEvent;
  	}

• sdk-java/core/src/main/java/io/cloudevents/core/v1/CloudEventBuilder.java

  Lines 113 to 130 in a3decf7

  	public CloudEvent build() {
  	if (id == null) {
  	throw createMissingAttributeException(ID);
  	}
  	if (source == null) {
  	throw createMissingAttributeException(SOURCE);
  	}
  	if (type == null) {
  	throw createMissingAttributeException(TYPE);
  	}
  	CloudEvent cloudEvent = new CloudEventV1(id, source, type, datacontenttype, dataschema, subject, time, this.data, this.extensions);
  	final CloudEventValidatorProvider validator = CloudEventValidatorProvider.getInstance();
  	validator.validate(cloudEvent);
  	return cloudEvent;
  	}

[pnt]

Yes, I’ll take a look at those. Along with tests, that should be it?

I've created a PR to fix this.