/**
   * Returns the value associated with {@code key} in this cache, first loading that value if
   * necessary. No observable state associated with this cache is modified until loading completes.
   *
   * <p>If another call to {@link #get} or {@link #getUnchecked} is currently loading the value for
   * {@code key}, simply waits for that thread to finish and returns its loaded value. Note that

      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(

   */
  ImmutableMap<K, V> getAllPresent(Iterable<? extends Object> keys);

  /**
   * Associates {@code value} with {@code key} in this cache. If the cache previously contained a
   * value associated with {@code key}, the old value is replaced by {@code value}.
   *
   * <p>Prefer {@link #get(Object, Callable)} when using the conventional "if cached, return;
   * otherwise create, cache and return" pattern.

        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);
    }
  }

  @ParametricNullness final K key;
  @ParametricNullness final V value;

  ImmutableEntry(@ParametricNullness K key, @ParametricNullness V value) {
    this.key = key;
    this.value = value;
  }

  @Override
  @ParametricNullness
  public final K getKey() {
    return key;
  }

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

  @Override
  @ParametricNullness

public class MapMergeTester<K, V> extends AbstractMapTester<K, V> {
  @MapFeature.Require(SUPPORTS_PUT)
  public void testAbsent() {
    assertEquals(
        "Map.merge(absent, value, function) should return value",
        v3(),
        getMap()
            .merge(
                k3(),
                v3(),
                (oldV, newV) -> {
                  throw new AssertionFailedError(

  }

  static final class Item<T> {
    final T value;
    final int groupNumber;
    final int itemNumber;

    Item(T value, int groupNumber, int itemNumber) {
      this.value = value;
      this.groupNumber = groupNumber;
      this.itemNumber = itemNumber;
    }

    @Override
    public String toString() {
      return value + " [group " + (groupNumber + 1) + ", item " + (itemNumber + 1) + ']';

            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();
      }
    },

  }

  /** Returns the associated value type. */
  @GwtIncompatible
  public Class<V> valueType() {
    return valueTypeOrObjectUnderJ2cl;
  }

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

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

  /**