Working of "Optional" attributes versus objects in a Published SOAP Webservice

Good afternoon,

I have a SOAP Webservice which has The following structure:

With this structure I would expect the following: Entity01 is always sent and has 0 to x Entity02 objects attached. If there are Entity02 objects, AttributeA should always be present and not empty. AttributeB is either left out or included and not empty.

When I use SoapUI to Test the Webservice, it accepts the request when I don't inlcude AttributeA in it. Am I overlooking something here? Could it be that because Entity02 is Optional, all underlying attributes are Optional as well? I would expect it to break due to the absence of AttributeA.

Thanks!