V oldValue = table.get(row, column);
    if (oldValue == null) {
      table.put(row, column, value);
    } else {
      V newValue = mergeFunction.apply(oldValue, value);
      if (newValue == null) {
        table.remove(row, column);
      } else {
        table.put(row, column, newValue);
      }
    }
  }

  private TableCollectors() {}

      V value = localCache.get(key);
      if (value != null) {
        return value;
      }

      try {
        V newValue = valueLoader.call();
        localCache.put(key, newValue);
        return newValue;
      } catch (Exception e) {
        throw new ExecutionException(e);
      }
    }

    @Override
    public @Nullable V getIfPresent(Object key) {

    assertNull(map.putInstance(Integer.class, new Integer(5)));

    Integer oldValue = map.putInstance(Integer.class, new Integer(7));
    assertEquals(5, (int) oldValue);

    Integer newValue = map.getInstance(Integer.class);
    assertEquals(7, (int) newValue);

    // Won't compile: map.putInstance(Double.class, new Long(42));
  }

  public void testNull() {

            String value1 = fessConfig.get(testKey);
            assertEquals(initialValue, value1);

            // Change system property
            String newValue = "changed";
            System.setProperty(Constants.FESS_CONFIG_PREFIX + testKey, newValue);

            // Get value again - in real FessConfigImpl it would be cached,
            // but our test implementation always checks system properties

    List<V> oldValues = getCopy(key);
    ListIterator<V> keyValues = new ValueForKeyIterator(key);
    Iterator<? extends V> newValues = values.iterator();

    // Replace existing values, if any.
    while (keyValues.hasNext() && newValues.hasNext()) {
      keyValues.next();
      keyValues.set(newValues.next());
    }

    // Remove remaining old values, if any.
    while (keyValues.hasNext()) {
      keyValues.next();

   */
  private void replaceValueInEntry(int entry, @ParametricNullness V newValue, boolean force) {
    checkArgument(entry != ABSENT);
    int newValueHash = Hashing.smearedHash(newValue);
    int newValueIndex = findEntryByValue(newValue, newValueHash);
    if (newValueIndex != ABSENT) {
      if (force) {
        removeEntryValueHashKnown(newValueIndex, newValueHash);

   */
  final void checkNoDuplicate(R rowKey, C columnKey, @Nullable V existingValue, V newValue) {
    checkArgument(
        existingValue == null,
        "Duplicate key: (row=%s, column=%s), values: [%s, %s].",
        rowKey,
        columnKey,
        newValue,
        existingValue);
  }

  // redeclare to satisfy our test for b/310253115
  @Override
  @J2ktIncompatible

    Integer oldValue = map.putInstance(Integer.class, Integer.valueOf(7));
    assertEquals(5, (int) oldValue);

    Integer newValue = map.getInstance(Integer.class);
    assertEquals(7, (int) newValue);
    assertEquals(7, (int) map.getInstance(TypeToken.of(Integer.class)));

    // Won't compile: map.putInstance(Double.class, new Long(42));
  }

  public void testNull() {

 *     }
 *     V result = value;
 *     value = null;
 *     notifyAll();
 *     return result;
 *   }
 *
 *   public synchronized void set(V newValue) throws InterruptedException {
 *     while (value != null) {
 *       wait();
 *     }
 *     value = newValue;
 *     notifyAll();
 *   }
 * }
 * }
 *
 * <h3>{@code ReentrantLock}</h3>
 *

    public void test_overwriteValues() {
        dataStoreParams.put("key1", "originalValue");
        assertEquals("originalValue", dataStoreParams.get("key1"));

        dataStoreParams.put("key1", "newValue");
        assertEquals("newValue", dataStoreParams.get("key1"));

        dataStoreParams.put("key1", null);
        assertNull(dataStoreParams.get("key1"));
    }

    // Test multiple operations in sequence