### Question:
ConfigValueMapView extends AbstractMap<String, String> { @Override public boolean containsKey(final Object key) { return delegate.containsKey(key); } ConfigValueMapView(final Map<String, ConfigValue> delegate); @Override int size(); @Override boolean isEmpty(); @Override boolean containsKey(final Object key); @Override boolean containsValue(final Object value); @Override String get(final Object key); @Override Set<String> keySet(); @Override Set<Map.Entry<String, String>> entrySet(); @Override Collection<String> values();  }### Answer:
@Test public void containsKey() { final Map<String, String> map = sampleMap(); assertTrue(map.containsKey("my.prop")); assertTrue(map.containsKey("my.null.value")); assertTrue(map.containsKey("my.null")); }