diff --git a/custom_routes.py b/custom_routes.py
index 7296884..bedb50e 100755
--- a/custom_routes.py
+++ b/custom_routes.py
@@ -55,7 +55,9 @@ def schema_validator(prompt):
         "outputs": {}
     }
     for node_id, node_info in prompt.items():
-        node_class_type = node_info["class_type"]
+        node_class_type = node_info.get("class_type")
+        if node_class_type is None:
+            raise NotImplementedError(f"Missing nodes founded, please first install the missing nodes using ComfyUI Manager")
         node_cls = NODE_CLASS_MAPPINGS[node_class_type]
         if hasattr(node_cls, "RELATIVE_PYTHON_MODULE") and node_cls.RELATIVE_PYTHON_MODULE == "custom_nodes.ComfyUI-ShellAgent-Plugin":
             schema = {}