private String getTimeZoneID(String tzID, String mzID) {
        String id = tzID;
        if (id == null) {
            assert (mzID != null);
            id = _tznames.getReferenceZoneID(mzID, getTargetRegion());
            if (id == null) {
                throw new IllegalArgumentException("Invalid mzID: " + mzID);
            }
        }
        return id;
    }
private String getTimeZoneID ( String tzID , String mzID ) { String id = tzID ; if ( id == null ) { assert ( mzID != null ) ; id = _tznames . getReferenceZoneID ( mzID , getTargetRegion ( ) ) ; if ( id == null ) { throw new IllegalArgumentException ( "Invalid mzID: " + mzID ) ; } } return id ; }
Private method returns a time zone ID. If tzID is not null, the value of tzID is returned.
If tzID is null, then this method look up a time zone ID for the current region. This is a
small helper method used by the parse implementation method

@param tzID
the time zone ID or null
@param mzID
the meta zone ID or null
@return A time zone ID
@throws IllegalArgumentException
when both tzID and mzID are null