### Question:
SentinelApacheHttpClientConfig { public void setPrefix(String prefix) { AssertUtil.notNull(prefix, "prefix cannot be null"); this.prefix = prefix; }  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 testConfigSetPrefix() { SentinelApacheHttpClientConfig config = new SentinelApacheHttpClientConfig(); config.setPrefix(null); }