public InterpreterResult hidePasswords(InterpreterResult ret) {
    if (ret == null) {
      return null;
    }
    return new InterpreterResult(ret.code(), replacePasswords(ret.message()));
  }
@Test
  void hidePasswordsNoResult() {
    UserCredentials userCredentials = mock(UserCredentials.class);
    CredentialInjector testee = new CredentialInjector(userCredentials);
    assertNull(testee.hidePasswords(null));
  }