"Should not contain null key after unsupported putAll(containsNullKey)");
  }

  @MapFeature.Require({SUPPORTS_PUT, ALLOWS_NULL_VALUES})
  public void testPutAll_nullValueSupported() {
    putAll(containsNullValue);
    expectAdded(containsNullValue.get(0));
  }

  @MapFeature.Require(value = SUPPORTS_PUT, absent = ALLOWS_NULL_VALUES)
  public void testPutAll_nullValueUnsupported() {

    GraphConnections<N, V> connectionsV = nodeConnections.get(nodeV);
    if (connectionsU == null || connectionsV == null) {
      return null;
    }

    V previousValue = connectionsU.removeSuccessor(nodeV);
    if (previousValue != null) {
      connectionsV.removePredecessor(nodeU);
      checkNonNegative(--edgeCount);
    }
    return previousValue;
  }

    }
  }

  /*
   * Preconditions.checkNotNull is *intended* for performing eager null checks on parameters that a
   * nullness checker can already "prove" are non-null. That means that the first parameter to
   * checkNotNull *should* be annotated to require it to be non-null.
   *
   * However, for a variety of reasons, Google developers have written a ton of code over the past

  }

  @CollectionFeature.Require(absent = ALLOWS_NULL_QUERIES)
  public void testContainsAll_nullNotAllowed() {
    try {
      assertFalse(collection.containsAll(MinimalCollection.of((E) null)));
    } catch (NullPointerException tolerated) {
    }
  }

  @CollectionFeature.Require(ALLOWS_NULL_QUERIES)
  public void testContainsAll_nullAllowed() {

      assertEquals((Character) 'b', table.get("bar", 1));
      assertNull(table.get("foo", 3));
      assertNull(table.remove(null, 1));
      assertNull(table.remove("foo", null));
      assertNull(table.remove(null, null));
      assertSize(2);
    } else {
      try {
        table.remove("foo", 3);
        fail();
      } catch (UnsupportedOperationException expected) {

  }

  @ListFeature.Require(SUPPORTS_ADD_WITH_INDEX)
  @CollectionFeature.Require(ALLOWS_NULL_VALUES)
  public void testAddAllAtIndex_nullSupported() {
    List<E> containsNull = singletonList(null);
    assertTrue("addAll(n, containsNull) should return true", getList().addAll(0, containsNull));
    /*
     * We need (E) to force interpretation of null as the single element of a
     * varargs array, not the array itself
     */

      checkMessage(expected);
    }
  }

  private static final String NON_NULL_STRING = "foo";

  public void testVerifyNotNull_simple_success() {
    String result = verifyNotNull(NON_NULL_STRING);
    assertSame(NON_NULL_STRING, result);
  }

  public void testVerifyNotNull_simple_failure() {
    try {
      verifyNotNull(null);
      fail();
    } catch (VerifyException expected) {
    }
  }

    graph.putEdgeValue(4, 4, "valueD");

    assertThat(graph.edgeValueOrDefault(1, 2, null)).isEqualTo("valueA");
    assertThat(graph.edgeValueOrDefault(2, 1, null)).isEqualTo("valueB");
    assertThat(graph.edgeValueOrDefault(2, 3, null)).isEqualTo("valueC");
    assertThat(graph.edgeValueOrDefault(4, 4, null)).isEqualTo("valueD");
    assertThat(graph.edgeValueOrDefault(1, 2, DEFAULT)).isEqualTo("valueA");

  @CollectionFeature.Require({SUPPORTS_REMOVE, ALLOWS_NULL_VALUES})
  @CollectionSize.Require(absent = ZERO)
  public void testRetainAll_containsNonNullWithNull() {
    initCollectionWithNullElement();
    expectReturnsTrue(disjoint);
    expectContents();
  }

  // retainAll(null)

  /*
   * AbstractCollection fails the retainAll(null) test when the subject

   * the call to {@code contains(null)} is permitted to throw a {@code NullPointerException}.
   *
   * @param message message to use upon assertion failure
   */
  protected void expectNullKeyMissingWhenNullKeysUnsupported(String message) {
    try {
      assertFalse(message, getMap().containsKey(null));
    } catch (NullPointerException tolerated) {