code: protected boolean containsRel100(Message message) {
  		ListIterator<SIPHeader> requireHeaders = message.getHeaders(RequireHeader.NAME);
  		if(requireHeaders != null) {
  			while (requireHeaders.hasNext()) {
  				if(REL100_OPTION_TAG.equals(requireHeaders.next().getValue())) {
  					return true;
  				}
  			}
  		}
  		ListIterator<SIPHeader> supportedHeaders = message.getHeaders(SupportedHeader.NAME);
  		if(supportedHeaders != null) {
  			while (supportedHeaders.hasNext()) {
  				if(REL100_OPTION_TAG.equals(supportedHeaders.next().getValue())) {
  					return true;
  				}
  			}
  		}
  		return false;
  	}
docs: we check all the values of Require and Supported headers to make sure the 100rel is present