public void unset(PropertyKey key) {
    Preconditions.checkNotNull(key, "key");
    mProperties.remove(key);
  }
@Test
  public void unset() {
    assertFalse(mConfiguration.isSet(PropertyKey.SECURITY_LOGIN_USERNAME));
    mConfiguration.set(PropertyKey.SECURITY_LOGIN_USERNAME, "test");
    assertTrue(mConfiguration.isSet(PropertyKey.SECURITY_LOGIN_USERNAME));
    mConfiguration.unset(PropertyKey.SECURITY_LOGIN_USERNAME);
    assertFalse(mConfiguration.isSet(PropertyKey.SECURITY_LOGIN_USERNAME));
  }