public void remove(PropertyKey key) {
    // remove is a nop if the key doesn't already exist
    if (mUserProps.containsKey(key)) {
      mUserProps.remove(key);
      mSources.remove(key);
      mHash.markOutdated();
    }
  }
@Test
  public void remove() {
    mProperties.remove(mKeyWithValue);
    assertEquals(mKeyWithValue.getDefaultValue(), mProperties.get(mKeyWithValue));
    assertEquals(Source.DEFAULT, mProperties.getSource(mKeyWithValue));
  }