diff --git a/fastapi/routing.py b/fastapi/routing.py
index 1098c1d03..6485b1ad5 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -546,7 +546,7 @@ class APIRoute(routing.Route):
             else:
                 response_model = return_annotation
         
-        if not lenient_issubclass(response_model, BaseModel):
+        if response_model is not None and not lenient_issubclass(response_model, BaseModel):
             inferred = infer_response_model_from_ast(endpoint)
             if inferred:
                 response_model = inferred
diff --git a/fastapi/utils.py b/fastapi/utils.py
index e5831c893..873c6343a 100644
--- a/fastapi/utils.py
+++ b/fastapi/utils.py
@@ -366,11 +366,22 @@ def infer_response_model_from_ast(
         return None
         
     return_stmt = None
-    for node in ast.walk(func_def):
+    
+
+    nodes_to_visit = list(func_def.body)
+    while nodes_to_visit:
+        node = nodes_to_visit.pop(0)
+        
         if isinstance(node, ast.Return):
             return_stmt = node
             break
             
+        if isinstance(node, (ast.FunctionDef, ast.AsyncFunctionDef, ast.ClassDef)):
+            continue
+            
+        for child in ast.iter_child_nodes(node):
+            nodes_to_visit.append(child)
+            
     if not return_stmt:
         return None
 
@@ -401,6 +412,10 @@ def infer_response_model_from_ast(
     for key, value in zip(dict_node.keys, dict_node.values):
         if not isinstance(key, ast.Constant):
             continue
+            
+        if not isinstance(key.value, str):
+            return None
+            
         field_name = key.value
         
         field_type = _infer_type_from_ast(
@@ -418,4 +433,7 @@ def infer_response_model_from_ast(
         from pydantic import create_model
 
     model_name = f"ResponseModel_{endpoint_function.__name__}"
-    return create_model(model_name, **fields)
+    try:
+        return create_model(model_name, **fields)
+    except Exception:
+        return None
diff --git a/tests/test_ast_inference.py b/tests/test_ast_inference.py
index 5867385ec..5e11fb09f 100644
--- a/tests/test_ast_inference.py
+++ b/tests/test_ast_inference.py
@@ -1,5 +1,13 @@
+import sys
+import os
+import uvicorn
+
+# Добавляем корень проекта в sys.path, чтобы Python видел пакет fastapi
+sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), '..')))
+
 from typing import Any, Dict, List
 from fastapi import FastAPI
+from fastapi.responses import JSONResponse
 from fastapi.testclient import TestClient
 
 app = FastAPI()
@@ -71,6 +79,21 @@ async def get_local_variable() -> Dict[str, Any]:
     }
     return response_data
 
+@app.get("/edge_cases/explicit_response")
+def get_explicit_response() -> JSONResponse:
+    return JSONResponse({"should_not_be_inferred": True})
+
+@app.get("/edge_cases/nested_function")
+async def get_nested_function() -> Dict[str, Any]:
+    def inner_function():
+        return {"inner": "value"}
+    
+    return {"outer": "value"}
+
+@app.get("/edge_cases/invalid_keys")
+def get_invalid_keys() -> Dict[Any, Any]:
+    return {1: "value", "valid": "key"}
+
 client = TestClient(app)
 
 def test_openapi_schema_ast_inference():
@@ -111,4 +134,22 @@ def test_openapi_schema_ast_inference():
     
     assert expr_props["calc_int"]["type"] == "integer"
     assert expr_props["calc_bool"]["type"] == "boolean"
-    
\ No newline at end of file
+
+    explicit_schema = paths["/edge_cases/explicit_response"]["get"]["responses"]["200"]["content"]["application/json"]["schema"]
+    assert "$ref" not in explicit_schema
+
+    nested_schema = paths["/edge_cases/nested_function"]["get"]["responses"]["200"]["content"]["application/json"]["schema"]
+    assert "$ref" in nested_schema
+    nested_ref = nested_schema["$ref"].split("/")[-1]
+    nested_props = schema["components"]["schemas"][nested_ref]["properties"]
+    assert "outer" in nested_props
+    assert "inner" not in nested_props
+
+    invalid_keys_schema = paths["/edge_cases/invalid_keys"]["get"]["responses"]["200"]["content"]["application/json"]["schema"]
+    assert "$ref" not in invalid_keys_schema
+
+if __name__ == "__main__":
+    # test_openapi_schema_ast_inference()
+    print("Запуск сервера для проверки Swagger UI...")
+    print("Откройте в браузере: http://127.0.0.1:8000/docs")
+    uvicorn.run(app, host="127.0.0.1", port=8000)