Currently there are no unit tests for web services and some of them fail.
One type of error is that of returning null:
rg.apache.cxf.interceptor.Fault: Cannot write part return. RPC/Literal parts cannot be null. (WS-I BP R2211)
These types are not allowed according to the spec.
See section 4.4.1
R2211 An ENVELOPE described with an rpc-literal binding MUST NOT have the xsi:nil attribute with a value of "1" or "true" on the part accessors.
If there are other issues that people are also witnessing I urge them to use this test framework to write a simple unit test that replicates the error they are expierencing.