Fixed potential NullPointerException in SharedEntityManagerCreator.

SharedEntityManagerCreator.createSharedEntityManager(EntityManagerFactory,
Map, boolean) now correctly forwards an empty array in case the
EntityManagerFactoryInfo returns null for the call to
….getEntityManagerInterface().

Previously the varargs invocation had turned null into an array with a
null value which caused a NullPointerException in the call to
Proxy.newProxyInstance(…) further down the call stack

Issue: SPR-10678