MULE-7502 - restoring constructor for backward compatibility and reverti...

...ng change in method signature that is not required
ExceptionListener will always be not null. Null only happens for SAP connector which is a must for backward compatibility of the connector. The issue fixed here won't apply to SAP connector but most likely users are not affected by this issue and there's no easy way to make the fix in SAP connector until we release a new version.