code: public static boolean isErrorCallbackNotImplemented(@Nullable Throwable t) {
  		return t != null && t.getClass().equals(ErrorCallbackNotImplemented.class);
  	}
docs: Check if the given error is a {@link #errorCallbackNotImplemented(Throwable) callback not implemented}
  exception, in which case its {@link Throwable#getCause() cause} will be the propagated
  error that couldn't be processed.
  
  @param t the {@link Throwable} error to check
  @return true if given {@link Throwable} is a callback not implemented exception.