code: @Implementation(minSdk = N)
    protected boolean isVoicemailVibrationEnabled(PhoneAccountHandle handle) {
      Boolean result = voicemailVibrationEnabledMap.get(handle);
      return result != null ? result : false;
    }
docs: Returns {@code null} by default or the value specified via {@link
  #setVoicemailVibrationEnabled(PhoneAccountHandle, boolean)}.