### Question:
DerivedAttributesMap extends ForwardingMap<String, String> { public static Map<String, String> of(Map<String, String> m) { if (m == null) { return null; } else { return new DerivedAttributesMap(m); } } private  DerivedAttributesMap(Map<String, String> attributes); static Map<String, String> of(Map<String, String> m); @Override String get(Object key); @Override String getOrDefault(Object key, String defaultValue); @Override boolean containsKey(@Nullable Object key);  }### Answer:
@Test public void testNullMap() { Map<String, String> attributes = null; Map<String, String> derived = DerivedAttributesMap.of(attributes); assertNull(derived); }