Fix adding semicolon to empty class

Author: haeter525

quark/core/struct/ruleobject.py

@@ -43,7 +43,8 @@ def __init__(self, ruleJson: os.PathLike, jsonData: dict = None) -> None:
 
         self._api = self._json_obj["api"]
         for index in range(len(self._api)):
-            if not self._api[index]["class"].endswith(";"):
+            if self._api[index]["class"] and \
+                    not self._api[index]["class"].endswith(";"):
                 self._api[index]["class"] += ";"
 
             # Check if the return type misses a semicolon at the end.