diff --git a/src/hebg/call_graph.py b/src/hebg/call_graph.py
index 28e24eb..a189620 100644
--- a/src/hebg/call_graph.py
+++ b/src/hebg/call_graph.py
@@ -64,7 +64,7 @@ def call_nodes(
                 # Search for name reference in all_behaviors
                 if node.name in heb_graph.all_behaviors:
                     node = heb_graph.all_behaviors[node.name]
-                if not hasattr(node, "graph"):
+                if not hasattr(node, "_graph") or node._graph is None:
                     action = node(observation)
                     break
                 self._extend_frontiere(node.graph.roots, heb_graph=node.graph)
diff --git a/tests/test_call_graph.py b/tests/test_call_graph.py
index 8958338..0cf048e 100644
--- a/tests/test_call_graph.py
+++ b/tests/test_call_graph.py
@@ -185,6 +185,7 @@ def build_graph(self) -> HEBGraph:
                 return graph
 
         sub_behavior = SubBehavior()
+        sub_behavior.graph
 
         root_behavior = RootBehavior()
         root_behavior.graph.all_behaviors["SubBehavior"] = sub_behavior