#301 voidType() value processing in buildSOAP

[Vsevolod Novikov]

When the voidType() value is passed as a value for 'kw' parameter of SOAPBuilder.buildSOAP(), it is processed incorrectly, probably because of lost 'return'. The lost 'return' is added in the applied patch.
The bug has been met using twisted.soap to process soap requests, when the voidType() value should be returned from the published method to return empty result.

[Vsevolod Novikov]

Patch fixing lost return