* track the problem back to its origin. A concrete example for such a source hint can be the file path or URL from
     * which the settings were read.
     *
     * @return the hint about the source of the problem or an empty string if unknown, never {@code null}
     */
    @Nonnull
    String getSource();

    /**

        List<MavenOptions> o = options.stream().filter(Objects::nonNull).toList();
        if (o.isEmpty()) {
            throw new IllegalArgumentException("No options specified (or all were null)");
        } else if (o.size() == 1) {
            return o.get(0);
        } else {
            return new LayeredMavenOptions<>(o);
        }
    }

    protected LayeredMavenOptions(List<O> options) {

        with(standardError) {
            files.forEach {
                assertContains("API changes in file '${it.name}' should be in alphabetical order (by type and member), yet these changes were not:\n")
            }
            changes?.forEach { assertContains(it.toString()) }
            assertContains(cleanupHint)
        }
    }

    private
    fun StringWriter.assertContains(text: String) {

   * with {@code FeatureSpecificTestSuiteBuilder.suppressing()} until <a
   * href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6409434">Sun bug 6409434</a> is fixed.
   * It's unclear whether nulls were to be permitted or forbidden, but presumably the eventual fix
   * will be to permit them, as it seems more likely that code would depend on that behavior than on

    }

    /**
     * The logic used here used to be a copy of the logic used in the DefaultArtifactCollector, and this method was
     * called right before the actual version/artifactScope changes were done. However, a different set of conditionals
     * (and more information) is needed to be able to determine when and if the version and/or artifactScope changes.

     *
     * @throws IllegalArgumentException if duplicate keys were added
     */
    public ImmutableMap<K, V> build() {
      return buildOrThrow();
    }

    /**
     * Returns a newly-created immutable map, or throws an exception if any key was added more than
     * once. The iteration order of the returned map is the order in which entries were inserted

          writePingFrame()
          return@schedule pingIntervalNanos
        }
      }
      if (messageAndCloseQueue.isNotEmpty()) {
        runWriter() // Send messages that were enqueued before we were connected.
      }
    }

    reader =
      WebSocketReader(
        isClient = streams.client,
        source = streams.source,
        frameCallback = this,

     *
     * @throws IllegalArgumentException if duplicate keys were added
     */
    public ImmutableMap<K, V> build() {
      return buildOrThrow();
    }

    /**
     * Returns a newly-created immutable map, or throws an exception if any key was added more than
     * once. The iteration order of the returned map is the order in which entries were inserted

    latch.countDown();

    exec.shutdown();
    exec.awaitTermination(100, MILLISECONDS);
  }

  /**
   * Tests that all listeners complete, even if they were added before or after the future was
   * finishing. Also acts as a concurrency test to make sure the locking is done correctly when a
   * future is finishing so that no listeners can be lost.
   */

	w.err = err
}

func (w *writerAt) Close() (err error) {
	switch {
	case len(w.buffer) > 0:
		err = errors.New("some file segments were not flushed from the queue")
		_ = w.w.CloseWithError(err)
	case w.err != nil:
		// No need to close here since both pipes were
		// closing inside TransferError()
		err = w.err
	default:
		err = w.w.Close()
	}
	for i := range w.buffer {
		delete(w.buffer, i)
	}