return column;
    }

    @Override
    public V getValue() {
      return value;
    }

    void merge(V value, BinaryOperator<V> mergeFunction) {
      checkNotNull(value, "value");
      this.value = checkNotNull(mergeFunction.apply(this.value, value), "mergeFunction.apply");
    }
  }

  private static <R extends @Nullable Object, C extends @Nullable Object, V> void mergeTables(

        K key = entry.getKey();
        if (duplicates.containsKey(key)) {
          V value = duplicates.get(key);
          if (value == null) {
            continue; // delete this duplicate
          }
          entry = new ImmutableMapEntry<>(key, value);
          duplicates.put(key, null);
        }
        newEntryArray[outI++] = entry;
      }
      entryArray = newEntryArray;

public class TreeTraverserTest extends TestCase {
  private static class Node {
    final char value;

    Node(char value) {
      this.value = value;
    }
  }

  private static final class Tree extends Node {
    final List<Tree> children;

    public Tree(char value, Tree... children) {
      super(value);
      this.children = Arrays.asList(children);
    }
  }

                }));
    expectAdded(e3());
  }

  @MapFeature.Require({SUPPORTS_PUT, ALLOWS_NULL_VALUES})
  @CollectionSize.Require(absent = ZERO)
  public void testMappedToNull() {
    initMapWithNullValue();
    assertEquals(
        "Map.merge(keyMappedToNull, value, function) should return value",
        v3(),
        getMap()
            .merge(
                getKeyForNullValue(),
                v3(),

            Lists.transform(keys, k -> Maps.immutableEntry(k, "dummy value")));
      }
    },
    BUILDER_PUT_ONE_BY_ONE {
      @Override
      public Map<Object, Object> create(List<?> keys) {
        ImmutableMap.Builder<Object, Object> builder = ImmutableMap.builder();
        for (Object k : keys) {
          builder.put(k, "dummy value");
        }
        return builder.buildOrThrow();
      }
    },

  @Override
  K checkKey(K key) {
    return checkNotNull(key);
  }

  @Override
  V checkValue(V value) {
    return checkNotNull(value);
  }

  /**
   * @serialData the key class, value class, number of entries, first key, first value, second key,
   *     second value, and so on.
   */
  @GwtIncompatible // java.io.ObjectOutputStream
  private void writeObject(ObjectOutputStream stream) throws IOException {

  private static final LazyLogger log = new LazyLogger(ImmediateFuture.class);

  @ParametricNullness private final V value;

  ImmediateFuture(@ParametricNullness V value) {
    this.value = value;
  }

  @Override
  @SuppressWarnings("CatchingUnchecked") // sneaky checked exception
  public void addListener(Runnable listener, Executor executor) {

    return connections;
  }

  @Override
  @CanIgnoreReturnValue
  @CheckForNull
  public V putEdgeValue(N nodeU, N nodeV, V value) {
    checkNotNull(nodeU, "nodeU");
    checkNotNull(nodeV, "nodeV");
    checkNotNull(value, "value");

    if (!allowsSelfLoops()) {
      checkArgument(!nodeU.equals(nodeV), SELF_LOOPS_NOT_ALLOWED, nodeU);
    }

    }
  }

  private static class Collider {
    final int value;

    Collider(int value) {
      this.value = value;
    }

    @Override
    public boolean equals(@Nullable Object obj) {
      return obj instanceof Collider && ((Collider) obj).value == value;
    }

    @Override
    public int hashCode() {
      return 1; // evil!
    }
  }

    }
  }

  private static class Collider {
    final int value;

    Collider(int value) {
      this.value = value;
    }

    @Override
    public boolean equals(@Nullable Object obj) {
      return obj instanceof Collider && ((Collider) obj).value == value;
    }

    @Override
    public int hashCode() {
      return 1; // evil!
    }
  }