code: public synchronized PacketBuilder withDouble(final double d)
      {
          checkBuilt();
          try
          {
              dataOutputStream.writeDouble(d);
          }
          catch (final IOException e)
          {
              logger.error("Unable to add double: {} : {}", e.getClass(), e.getMessage());
          }
          return this;
      }
docs: Adds a double
  @param d Double
  @throws IllegalStateException see {@link #checkBuilt()}