### Question:
SentinelApacheHttpClientConfig { public void setFallback(ApacheHttpClientFallback fallback) { AssertUtil.notNull(fallback, "fallback cannot be null"); this.fallback = fallback; }  String getPrefix(); void setPrefix(String prefix); ApacheHttpClientResourceExtractor getExtractor(); void setExtractor(ApacheHttpClientResourceExtractor extractor); ApacheHttpClientFallback getFallback(); void setFallback(ApacheHttpClientFallback fallback);  }### Answer:
@Test(expected = IllegalArgumentException.class) public void testConfigSetFallback() { SentinelApacheHttpClientConfig config = new SentinelApacheHttpClientConfig(); config.setFallback(null); }