return entry.getKey();
          }
        };
      }

      @Override
      public int size() {
        return backingMap.size();
      }

      @Override
      public boolean contains(@CheckForNull Object key) {
        return containsKey(key);
      }
    };
  }

  // Internal methods (package-visible, but treat as only subclass-visible)

  @CheckForNull

 *       you can set {@code
 *       -XepOpt:NullAway:CustomNullableAnnotations=com.google.common.base.ParametricNullness,...,com.google.common.util.concurrent.ParametricNullness},
 *       where the {@code ...} contains the names of all the other {@code ParametricNullness}
 *       annotations in Guava. Or you might prefer to omit Guava from your {@code AnnotatedPackages}
 *       list.

   * {@code node}'s incoming edges <i>against</i> the direction (if any) of the edge.
   *
   * <p>Some algorithms that operate on a {@code PredecessorsFunction} may produce undesired results
   * if the returned {@link Iterable} contains duplicate elements. Implementations of such
   * algorithms should document their behavior in the presence of duplicates.
   *
   * <p>The elements of the returned {@code Iterable} must each be:
   *
   * <ul>

 *       you can set {@code
 *       -XepOpt:NullAway:CustomNullableAnnotations=com.google.common.base.ParametricNullness,...,com.google.common.util.concurrent.ParametricNullness},
 *       where the {@code ...} contains the names of all the other {@code ParametricNullness}
 *       annotations in Guava. Or you might prefer to omit Guava from your {@code AnnotatedPackages}
 *       list.

 *       you can set {@code
 *       -XepOpt:NullAway:CustomNullableAnnotations=com.google.common.base.ParametricNullness,...,com.google.common.util.concurrent.ParametricNullness},
 *       where the {@code ...} contains the names of all the other {@code ParametricNullness}
 *       annotations in Guava. Or you might prefer to omit Guava from your {@code AnnotatedPackages}
 *       list.

 *       you can set {@code
 *       -XepOpt:NullAway:CustomNullableAnnotations=com.google.common.base.ParametricNullness,...,com.google.common.util.concurrent.ParametricNullness},
 *       where the {@code ...} contains the names of all the other {@code ParametricNullness}
 *       annotations in Guava. Or you might prefer to omit Guava from your {@code AnnotatedPackages}
 *       list.

    public void test_updateConfiguration() {
        assertNotNull(systemHelper.updateConfiguration());
        systemHelper.addUpdateConfigListener("XXX", () -> "OK");
        assertTrue(systemHelper.updateConfiguration().contains("XXX: OK"));
    }

    public void test_isChangedClusterState() {
        systemHelper.isChangedClusterState(0);
        assertFalse(systemHelper.isChangedClusterState(0));

            KeyPresentBehavior.ANY_PRESENT,
            KeyAbsentBehavior.NEXT_LOWER);
    if (index == -1) {
      return null;
    } else {
      Range<K> range = ranges.get(index);
      return range.contains(key) ? values.get(index) : null;
    }
  }

  @Override
  @CheckForNull
  public Entry<Range<K>, V> getEntry(K key) {
    int index =
        SortedLists.binarySearch(
            ranges,

      } else {
        break;
      }
      iterations++;
      if (iterations >= maxIterations) {
        @SuppressWarnings("nullness") // safe because we pass sort() a range that contains real Ts
        T[] castBuffer = (T[]) buffer;
        // We've already taken O(k log k), let's make sure we don't take longer than O(k log k).
        sort(castBuffer, left, right + 1, comparator);
        break;

    Future<?> second = serializer.submitAsync(secondCallable, directExecutor());
    assertThat(secondCallable.called).isFalse();
    assertThat(second.toString()).contains(secondCallable.toString());
    firstFuture.set(null);
    assertThat(second.toString()).contains(secondCallable.future.toString());
  }

  private static class BlockingCallable implements Callable<@Nullable Void> {