@Test(expected = NullPointerException.class)
 public void testPutNull() {
   _metadataRepo.putMetricTTL(null, 3);
   fail("Unexpected absence of NullPointerException");
 }
 @Before
 public void setUp() {
   _metadataRepo = new MessageHandlerChain();
   _metadataRepo.putMetricTTL(AVAILABLE_ID, AVAILABLE_TTL);
 }