| None

Author: mscroggs

src/causalprog/_abc/labelled.py

@@ -12,11 +12,14 @@ class Labelled(ABC):
     """
 
     __slots__ = ("_label",)
-    _label: str
+    _label: str | None
 
     @property
     def label(self) -> str:
         """Label of this object."""
+        if self._label is None:
+            msg = "Node has no label."
+            raise ValueError(msg)
         return self._label
 
     def __init__(self, *, label: str | None) -> None: