question: private void attachHeader ( SIPHeader h ) { if ( h == null ) throw new IllegalArgumentException ( "null header!" ) ; try { if ( h instanceof SIPHeaderList ) { SIPHeaderList < ? > hl = ( SIPHeaderList < ? > ) h ; if ( hl . isEmpty ( ) ) { return ; } } attachHeader ( h , false , false ) ; } catch ( SIPDuplicateHeaderException ex ) { } }
target:  Attach a header and die if you get a duplicate header exception.