public V put(K key, V value) {
    return resolve(map.put(key, new WeakReference<>(value)));
  }
@Test
  public void testPruneNullEntries() {
    referenceMap.put(1, "1");
    assertPruned(0);
    referenceMap.put(2, null);
    assertMapSize(2);
    assertPruned(1);
    assertMapSize(1);
    assertMapDoesNotContainKey(2);
    assertMapEntryEquals(1, "1");
    assertLostCount(1);
  }