test(guard): 补 assertNotNull 静态导入

Author: loong10k

src/test/java/io/github/easy4j/hermes/util/EndpointGuardTest.java

@@ -17,6 +17,7 @@
 
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;