RH-SSO handles empty POST data incorrectly while invoking admin REST interfaces

Issue

• When making POST requests to /users and /groups REST interfaces with empty data RH-SSO returns HTTP/1.1 500 Internal server error.

• RH-SSO currently produces an uncaught java.lang.NullPointerException with empty POST data while invoking admin REST interfaces which is not just an extremely bad programming style but a sign for unwanted after effects.

• RH-SSO is vulnerable against bad requests with none/empty post data.