diff --git a/wizard-work/beam/toposort/toposort.py b/wizard-work/beam/toposort/toposort.py
index de77f22..4da0d8e 100644
--- a/wizard-work/beam/toposort/toposort.py
+++ b/wizard-work/beam/toposort/toposort.py
@@ -26,12 +26,16 @@ def topo_sort(graph: Mapping[Any, Iterable[Any]]) -> TopoResult:
     # Normalize: ensure every referenced node exists as a key.
     nodes: set[Any] = set(graph.keys())
     for deps in graph.values():
+        if deps is None:
+            continue
         for d in deps:
             nodes.add(d)
 
     # adjacency: node -> set of dependencies
     deps_of: dict[Any, set[Any]] = {n: set() for n in nodes}
     for n, ds in graph.items():
+        if ds is None:
+            ds = []
         for d in ds:
             if d == n:
                 # self-loop is a cycle of length 1