Implement Message.__bool__ for danielgtaylor#130

Author: Gobot1234

src/betterproto/__init__.py

@@ -554,6 +554,12 @@ def __setattr__(self, attr: str, value: Any) -> None:
 
         super().__setattr__(attr, value)
 
+    def __bool__(self) -> bool:
+        return any(
+            self.__raw_get(field_name) is not PLACEHOLDER
+            for field_name in self._betterproto.meta_by_field_name
+        )
+
     @property
     def _betterproto(self):
         """