Update src/pytorch_lightning/loggers/logger.py

Author: carmocca

src/pytorch_lightning/loggers/logger.py

@@ -208,7 +208,7 @@ def name(self) -> Optional[str]:
 
     @property
     @abstractmethod
-    def version(self) -> Union[int, str, None]:
+    def version(self) -> Optional[Union[int, str]]:
         """Return the experiment version."""