DocMap docMap = new DocMap(parentMap);

        docMap.put("nullKey", null);
        assertTrue(docMap.containsKey("nullKey"));
        assertTrue(docMap.containsValue(null));
        assertNull(docMap.get("nullKey"));

        assertNull(docMap.put("nullKey", "newValue"));
        assertEquals("newValue", docMap.get("nullKey"));
    }

    public void test_map_interface_compliance() {

    }

    // Test getAsString with null value
    public void test_getAsStringWithNullValue() {
        dataStoreParams.put("nullKey", null);
        assertNull(dataStoreParams.getAsString("nullKey"));
    }

    // Test getAsString for non-existent key
    public void test_getAsStringNonExistentKey() {
        assertNull(dataStoreParams.getAsString("nonexistent"));
    }

  }

  public void testOfEntriesNull() {
    Entry<@Nullable Integer, Integer> nullKey = entry(null, 23);
    assertThrows(
        NullPointerException.class,
        () -> ImmutableBiMap.ofEntries((Entry<Integer, Integer>) nullKey));
    Entry<Integer, @Nullable Integer> nullValue =
        ImmutableBiMapTest.<@Nullable Integer>entry(23, null);
    assertThrows(

        .testEquals();
  }

  public void testOfEntriesNull() {
    Entry<@Nullable Integer, @Nullable Integer> nullKey = entry(null, 23);
    assertThrows(
        NullPointerException.class,
        () -> ImmutableMap.ofEntries((Entry<Integer, Integer>) nullKey));
    Entry<@Nullable Integer, @Nullable Integer> nullValue = entry(23, null);
    assertThrows(
        NullPointerException.class,

        try {
            WebApiUtil.setObject("validKey", "validValue");
            WebApiUtil.setObject("", "emptyKey");
            WebApiUtil.setObject("nullValue", null);
            WebApiUtil.setObject(null, "nullKey");
            WebApiUtil.setObject(null, null);
        } catch (Exception e) {
            fail("setObject should handle parameter validation gracefully: " + e.getMessage());
        }

       * lets all futures share the same listener.
       *
       * We store `localFuturesOrNull` inside the listener because `this.futures` might be nulled
       * out by the time the listener runs for the final future -- at which point we need to check
       * all inputs for exceptions *if* we're collecting values. If we're not, then the listener

        }
      }

      @Override
      public Entry<E> next() {
        if (!hasNext()) {
          throw new NoSuchElementException();
        }
        // requireNonNull is safe because current is only nulled out after iteration is complete.
        Entry<E> result = wrapEntry(requireNonNull(current));
        prevEntry = result;
        if (current.succ() == header) {
          current = null;
        } else {