Fix serializer validation in CreateResourceProcessor if serializer is not defined.
Fix serializer validation in CreateResourceProcessor if serializer is not defined.

opennode/waldur-mastermind,opennode/nodeconductor-assembly-waldur,opennode/waldur-mastermind,opennode/waldur-mastermind,opennode/waldur-mastermind,opennode/nodeconductor-assembly-waldur,opennode/nodeconductor-assembly-waldur