ResultCursorsHolder { public void add( CompletionStage<? extends FailableCursor> cursorStage ) { Objects.requireNonNull( cursorStage ); cursorStages.add( cursorStage ); }  void add( CompletionStage<? extends FailableCursor> cursorStage );  }
@Test void shouldFailToAddNullCursorStage() { ResultCursorsHolder holder = new ResultCursorsHolder(); assertThrows( NullPointerException.class, () -> holder.add( null ) ); }