Check for a behavior change on Response.readEntity()

This rule flags Java code that calls the javax.ws.rs.core.Response.readEntity() method because it behaves differently when the response entity is empty.

Although the method signatures did not change, the method implementations behave differently when the entity included in the response is empty. The jaxrs-2.0 and jaxrs-2.1 features throw an IllegalStateException when the entity is empty. The restfulws-3.0 feature returns an empty String object when the entity is empty. These behavior changes do not cause compilation errors because the return type of the method is not changed. For further information, see Differences between Jakarta EE 9.1 and 8.0.