code: @SuppressWarnings("rawtypes")
  	public static Class<?> getCollectionType(Class<? extends Collection> collectionClass) {
  		return ResolvableType.forClass(collectionClass).asCollection().resolveGeneric();
  	}
docs: Determine the generic element type of the given Collection class
  (if it declares one through a generic superclass or generic interface).
  @param collectionClass the collection class to introspect
  @return the generic type, or {@code null} if none