style(common): 允许 isLocalServer 传递空值参数

hamster-ball-common/src/main/java/cn/hamster3/mc/plugin/ball/common/api/BallAPI.java

@@ -329,7 +329,7 @@ public abstract class BallAPI {
      * @param serverID 服务器ID
      * @return true 代表该服务器信息是本服服务器
      */
-    public boolean isLocalServer(@NotNull String serverID) {
+    public boolean isLocalServer(@Nullable String serverID) {
         return getLocalServerId().equalsIgnoreCase(serverID);
     }