execution_time can return None

b_asic/operation.py

@@ -890,9 +890,7 @@ class AbstractOperation(Operation, AbstractGraphComponent):
                 )
 
     @property
-    def execution_time(self) -> int:
-        if self._execution_time is None:
-            raise ValueError("No execution time specified.")
+    def execution_time(self) -> Optional[int]:
         return self._execution_time
 
     @execution_time.setter

b_asic/scheduler_gui/graphics_component_item.py

@@ -229,7 +229,7 @@ class GraphicsComponentItem(QGraphicsItemGroup):
         self._label_item.setPos(self._component_item.pos() + center)
 
         ## execution time
-        if self._operation.execution_time:
+        if self._operation.execution_time is not None:
             self._execution_time_item = QGraphicsRectItem(
                 0, 0, self._operation.execution_time, self._height
             )