@Override
  public Optional<ActiveRule> get(RuleKey ruleKey) {
    checkState(activeRulesByKey != null, "Active rules have not been initialized yet");
    return Optional.ofNullable(activeRulesByKey.get(ruleKey));
  }
@Test
  public void can_not_get_if_not_initialized() {
    assertThatThrownBy(() -> underTest.get(RULE_KEY))
      .isInstanceOf(IllegalStateException.class)
      .hasMessage("Active rules have not been initialized yet");
  }