// null key
    DummyEntry<Object, Object> nullEntry = DummyEntry.create(null, hash, entry);
    Object nullValue = new Object();
    ValueReference<Object, Object> nullValueRef = map.newValueReference(nullEntry, nullValue, 1);
    nullEntry.setValueReference(nullValueRef);
    table.set(index, nullEntry);
    // skip the null key

    // null key
    DummyEntry<Object, Object> nullEntry = DummyEntry.create(null, hash, entry);
    Object nullValue = new Object();
    ValueReference<Object, Object> nullValueRef = map.newValueReference(nullEntry, nullValue, 1);
    nullEntry.setValueReference(nullValueRef);
    table.set(index, nullEntry);
    // skip the null key

    boolean nullKeys = inverseFeatures.remove(MapFeature.ALLOWS_NULL_KEYS);
    boolean nullValues = inverseFeatures.remove(MapFeature.ALLOWS_NULL_VALUES);

    if (nullKeys) {
      inverseFeatures.add(MapFeature.ALLOWS_NULL_VALUES);
    }
    if (nullValues) {
      inverseFeatures.add(MapFeature.ALLOWS_NULL_KEYS);
    }

    inverseFeatures.add(NoRecurse.INVERSE);

        sourceMap.put("string", "test");
        sourceMap.put("integer", 42);
        sourceMap.put("long", 100L);
        sourceMap.put("double", 3.14);
        sourceMap.put("boolean", false);
        sourceMap.put("null_value", null);
        sourceMap.put("nested", nestedMap);

        event.setSourceMap(sourceMap);

        Map<String, Object> result = event.toSource();
        assertEquals("test", result.get("string"));

    boolean nullKeys = inverseFeatures.remove(MapFeature.ALLOWS_NULL_KEYS);
    boolean nullValues = inverseFeatures.remove(MapFeature.ALLOWS_NULL_VALUES);

    if (nullKeys) {
      inverseFeatures.add(MapFeature.ALLOWS_NULL_VALUES);
    }
    if (nullValues) {
      inverseFeatures.add(MapFeature.ALLOWS_NULL_KEYS);
    }

    inverseFeatures.add(NoRecurse.INVERSE);

        assertEquals(1, intValues.length);
        assertEquals("123", intValues[0]);

        String[] nullValues = defaultContentsParser.getFieldValues(document, "non_existent");
        assertEquals(0, nullValues.length);
    }

    @Test
    public void test_parseSearchWords() throws Exception {
        String[] words = new String[] { "検索", "エンジン" };