code: function BlockPacket(block, witness) {
    if (!(this instanceof BlockPacket))
      return new BlockPacket(block, witness);
  
    Packet.call(this);
  
    this.block = block || new MemBlock();
    this.witness = witness || false;
  }
docs: Represents a `block` packet.
  @constructor
  @param {Block|null} block
  @param {Boolean?} witness
  @property {Block} block
  @property {Boolean} witness