code: protected static boolean writeCustomType(Output out, Object obj) {
          if (out.isCustom(obj)) {
              // Write custom data
              out.writeCustom(obj);
              return true;
          } else {
              return false;
          }
      }
docs: Writes a custom data to the output
  
  @param out
  Output writer
  @param obj
  Custom data
  @return <tt>true</tt> if the object has been written, otherwise <tt>false</tt>