code: @Override
      public Packet getNextPacket() throws IOException {
          final Object content = parseSipContent();
          if (content instanceof SDP) {
              return new SDPPacketImpl(this, (SDP)content);
          }
          return null;
      }
docs: /*
  (non-Javadoc)
  
  @see io.pkts.packet.Packet#getNextPacket()