Calling TransactionImple to register synchronization with null parameter causes NullPointerException being thrown when trace logging is enabled

If trace logging is enabled then call on com.arjuna.ats.internal.jta.transaction.jts.TransactionImple#registerSynchronization is done with null in parameter then NullPointerException is thrown but SystemException should be thrown in such case.

https://github.com/jbosstm/narayana/blob/930bd7f17f1b0cc2b8529eaa2ae1fcacf9582ac5/ArjunaJTS/jtax/classes/com/arjuna/ats/internal/jta/transaction/jts/TransactionImple.java#L452