refactor: Reflect changes in Cluster class
diff --git a/diagrams/__init__.py b/diagrams/__init__.py
index 1fb33db73..33520175e 100644
--- a/diagrams/__init__.py
+++ b/diagrams/__init__.py
@@ -258,11 +258,8 @@ def __exit__(self, exc_type, exc_value, traceback):
             self._diagram.subgraph(self.dot)
         setcluster(self._parent)
 
-    def _validate_direction(self, direction: str):
-        direction = direction.upper()
-        if direction in self.__directions:
-            return True
-        return False
+    def _validate_direction(self, direction: str) -> bool:
+        return direction.upper() in self.__directions
 
     def node(self, nodeid: str, label: str, **attrs) -> None:
         """Create a new node in the cluster."""

Refactor the _validate_direction in Cluster class I mess it when I made the changes in the 592 PR https://github.com/mingrammer/diagrams/pull/592