Apply suggestions from code review

Co-authored-by: William FH <13333726+hinthornw@users.noreply.github.com>

libs/langgraph/langgraph/graph/graph.py

@@ -194,7 +194,7 @@ class Graph:
                     "Node name must be provided if action is not a function"
                 )
         if action is None:
-            raise RuntimeError
+            raise RuntimeError(f"Expected a function or Runnable action in add_node. Received None.")
         if node in self.nodes:
             raise ValueError(f"Node `{node}` already present.")
         if node == END or node == START:

libs/langgraph/langgraph/graph/state.py

@@ -320,7 +320,7 @@ class StateGraph(Graph):
             )
         if not isinstance(node, str):
             action = node
-            node = getattr(action, "name", getattr(action, "__name__"))
+            node = getattr(action, "name", getattr(action, "__name__", None))
             if node is None:
                 raise ValueError(
                     "Node name must be provided if action is not a function"