Add typing, renaming, convenience methods/properties

b_asic/signal.py

@@ -82,12 +82,14 @@ class Signal(AbstractGraphComponent):
         """Return the source Operation of the signal."""
         if self._source is not None:
             return self._source.operation
+        return None
 
     @property
     def destination_operation(self) -> Optional["Operation"]:
         """Return the destination Operation of the signal."""
         if self._destination is not None:
             return self._destination.operation
+        return None
 
     def set_source(self, source: Union["OutputPort", "Signal", "Operation"]) -> None:
         """