diff --git a/src/main/java/pw/yumc/YumCore/utils/Assert.java b/src/main/java/pw/yumc/YumCore/utils/Assert.java
index fe0be7c..0697a6a 100644
--- a/src/main/java/pw/yumc/YumCore/utils/Assert.java
+++ b/src/main/java/pw/yumc/YumCore/utils/Assert.java
@@ -41,6 +41,6 @@ public class Assert<T> {
     }
 
     public void runIsAssignable(Class clazz, Consumer<? super T> consumer) {
-        runIsTrue(clazz.isAssignableFrom(t.getClass()), () -> consumer.accept(t));
+        runIsTrue(t != null && clazz.isAssignableFrom(t.getClass()), () -> consumer.accept(t));
     }
 }
\ No newline at end of file
diff --git a/src/test/java/pw/yumc/YumCore/mc/ServerPingTest.java b/src/test/java/pw/yumc/YumCore/mc/ServerPingTest.java
index be26d34..4b1c1d2 100644
--- a/src/test/java/pw/yumc/YumCore/mc/ServerPingTest.java
+++ b/src/test/java/pw/yumc/YumCore/mc/ServerPingTest.java
@@ -14,7 +14,7 @@ import pw.yumc.YumCore.bukkit.Log;
 public class ServerPingTest {
     @Test
     public void test() {
-        val ping = new ServerPing("server.yumc.pw");
+        val ping = new ServerPing("play.i5mc.com");
         ping.fetchData();
         Log.i("version: %s max: %s online: %s motd: %s",
               ping.getVersionName(), ping.getPlayersMax(), ping.getPlayersOnline(), ping.getMotd());