/**
 * An immutable object that may contain a non-null reference to another object. Each instance of
 * this type either contains a non-null reference, or contains nothing (in which case we say that
 * the reference is "absent"); it is never said to "contain {@code null}".
 *
 * <p>A non-null {@code Optional<T>} reference can be used as a replacement for a nullable {@code T}

    if (adjacentNodes != null) {
      checkState(adjacentNodes.add(node));
    }
  }

  private static <T> @Nullable T getReference(@Nullable Reference<T> reference) {
    return (reference == null) ? null : reference.get();
  }

		nrules[pattern] = nrules[pattern].Union(targetIDSet)
	}

	return nrules
}

// Difference - returns difference with given rules as new rules.
func (rules Rules) Difference(rules2 Rules) Rules {
	nrules := make(Rules)

	for pattern, targetIDSet := range rules {
		if nv := targetIDSet.Difference(rules2[pattern]); len(nv) > 0 {
			nrules[pattern] = nv
		}
	}

	return nrules

    }

    @Override
    public void finalizeReferent() {
      finalizeReferentCalled = true;
    }
  }

  /**
   * Keeps a weak reference to the underlying reference queue. When this reference is cleared, we
   * know that the background thread has stopped and released its strong reference.
   */
  private WeakReference<ReferenceQueue<Object>> queueReference;

  @Test
  public void testThatFinalizerStops() {

    private String message;

    private String reference;

    private List<ExceptionSummary> children;

    public ExceptionSummary(Throwable exception, String message, String reference) {
        this(exception, message, reference, null);
    }

    public ExceptionSummary(Throwable exception, String message, String reference, List<ExceptionSummary> children) {
        this.exception = exception;

  public static <T> T verifyNotNull(@Nullable T reference) {
    return verifyNotNull(reference, "expected a non-null reference");
  }

  /**
   * Ensures that {@code reference} is non-null, throwing a {@code VerifyException} with a custom
   * message otherwise.
   *
   * @param errorMessageTemplate a template for the exception message should the check fail. The

    if (threadStarted) {
      return;
    }

    Reference<?> reference;
    while ((reference = queue.poll()) != null) {
      /*
       * This is for the benefit of phantom references. Weak and soft references will have already
       * been cleared by this point.
       */
      reference.clear();
      try {
        ((FinalizableReference) reference).finalizeReferent();
      } catch (Throwable t) {

/**
 * An immutable object that may contain a non-null reference to another object. Each instance of
 * this type either contains a non-null reference, or contains nothing (in which case we say that
 * the reference is "absent"); it is never said to "contain {@code null}".
 *
 * <p>A non-null {@code Optional<T>} reference can be used as a replacement for a nullable {@code T}

class Components(BaseModelWithConfig):
    schemas: dict[str, Schema | Reference] | None = None
    responses: dict[str, Response | Reference] | None = None
    parameters: dict[str, Parameter | Reference] | None = None
    examples: dict[str, Example | Reference] | None = None
    requestBodies: dict[str, RequestBody | Reference] | None = None
    headers: dict[str, Header | Reference] | None = None

    @DisplayName("toByteArray returns mechanismToken reference when present")
    void toByteArrayReturnsToken() throws IOException {
        TestSpnegoToken t = new TestSpnegoToken();
        byte[] raw = new byte[] { 11, 12, 13 };
        t.parse(raw);
        // Current behavior of test impl: returns same reference
        assertSame(raw, t.toByteArray(), "should return the same reference as mechanismToken");
    }

    @Test