code: public static void writeLong(final ObjectOutput out, final Long l)
              throws IOException {
          if (l == null) {
              out.writeByte(0);
              return;
          }
          out.writeByte(1);
          out.writeLong(l);
      }
docs: Writes the {@link Long} to the output.
  <p>
  This method and its equivalent {@link #readLong(ObjectInput)
  read-variant} store {@code l} in a more efficient way than serializing
  the {@link Long} class.
  </p>
  
  @param out Non-null {@link ObjectOutput}
  @param l {@link Long}; may be null
  @throws IOException Thrown if an I/O error occurred
  @see #readLong(ObjectInput)