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"));

    assertThrows(NullPointerException.class, () -> ImmutableClassToInstanceMap.copyOf(nullKey));

    Map<? extends Class<? extends Number>, Number> nullValue = singletonMap(Number.class, null);
    assertThrows(NullPointerException.class, () -> ImmutableClassToInstanceMap.copyOf(nullValue));
  }

  public void testCopyOf_imap_empty() {
    Map<Class<?>, Object> in = emptyMap();

        assertEquals("present", presentOptional.get());
        assertEquals("present", presentOptional.orElse("default"));

        // Test with null value
        String nullValue = null;
        OptionalEntity<String> emptyOptional = OptionalUtil.ofNullable(nullValue);

        assertFalse(emptyOptional.isPresent());
        assertEquals("default", emptyOptional.orElse("default"));

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

  private static <T extends @Nullable Object> Entry<T, T> entry(T key, T value) {

      boolean permitsDuplicates,
      @Nullable String nullKey,
      @Nullable Integer nullValue) {
    multimap.clear();
    multimap.put("foo", 1);
    multimap.put("foo", 2);
    multimap.put("foo", 3);
    multimap.put("bar", 5);
    multimap.put("bar", -1);
    multimap.put(nullKey, nullValue);
    multimap.put("foo", nullValue);
    multimap.put(nullKey, 5);
    multimap.put("foo", 2);

    // null key
    InternalEntry<Object, Object, ?> nullEntry = segment.newEntryForTesting(null, hash, entry);
    Object nullValue = new Object();
    WeakValueReference<Object, Object, ?> nullValueRef =
        segment.newWeakValueReferenceForTesting(nullEntry, nullValue);
    segment.setWeakValueReferenceForTesting(nullEntry, nullValueRef);
    segment.setTableEntryForTesting(index, nullEntry);
    // skip the null key

    // null key
    InternalEntry<Object, Object, ?> nullEntry = segment.newEntryForTesting(null, hash, entry);
    Object nullValue = new Object();
    WeakValueReference<Object, Object, ?> nullValueRef =
        segment.newWeakValueReferenceForTesting(nullEntry, nullValue);
    segment.setWeakValueReferenceForTesting(nullEntry, nullValueRef);
    segment.setTableEntryForTesting(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

    // 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