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issue: mcpo failed with TypeError and NameError when running with Neo4j MCP server #198

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issue: mcpo failed with TypeError and NameError when running with Neo4j MCP server#198
#200
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bugSomething isn't working
@yohei1126

Description

@yohei1126
yohei1126
opened on Jul 14, 2025

Check Existing Issues

  • I have searched the existing issues and discussions.
  • I am using the latest version of mcpo.

mcpo Version

0.0.16

Open WebUI Version (if applicable)

No response

Operating System

macOS

Browser (if applicable)

No response

Confirmation

  • I have read and followed all instructions in README.md.
  • I am using the latest version of both MCPO and Open WebUI.
  • I have included the browser console logs.
  • I have included the Docker container logs.
  • I have listed steps to reproduce the bug in detail.

Expected Behavior

$ cat ~/work/config.json 
{
  "mcpServers": {
    "time": {
      "command": "uvx",
      "args": ["mcp-server-time", "--local-timezone=America/New_York"]
    },
    "neo4j-cypher": {
      "command": "uvx",
      "args": [
        "mcp-neo4j-cypher",
        "--db-url", "bolt://localhost:7687",
        "--username", "neo4j",
        "--password", "password123",
        "--namespace", "lineage"
      ]
    }
  }
}
$ uv run mcpo --config ~/work/config.json 
Starting MCP OpenAPI Proxy with config file: /xxx/work/config.json
2025-07-14 15:30:52,537 - INFO - Starting MCPO Server...
2025-07-14 15:30:52,538 - INFO -   Name: MCP OpenAPI Proxy
2025-07-14 15:30:52,538 - INFO -   Version: 1.0
2025-07-14 15:30:52,538 - INFO -   Description: Automatically generated API from MCP Tool Schemas
2025-07-14 15:30:52,538 - INFO -   Hostname: XP43WG00FM
2025-07-14 15:30:52,538 - INFO -   Port: 8000
2025-07-14 15:30:52,538 - INFO -   API Key: Not Provided
2025-07-14 15:30:52,538 - INFO -   CORS Allowed Origins: ['*']
2025-07-14 15:30:52,538 - INFO -   Path Prefix: /
2025-07-14 15:30:52,539 - INFO - Loading MCP server configurations from: /Users/yohei.onishi/work/config.json
2025-07-14 15:30:52,539 - INFO - Configured MCP Servers:
2025-07-14 15:30:52,539 - INFO -   Configuring Stdio MCP Server 'time' with command: uvx with args: ['mcp-server-time', '--local-timezone=America/New_York']
2025-07-14 15:30:52,540 - INFO -   Configuring Stdio MCP Server 'neo4j-cypher' with command: uvx with args: ['mcp-neo4j-cypher', '--db-url', 'bolt://localhost:7687', '--username', 'neo4j', '--password', 'password123', '--namespace', 'lineage']
2025-07-14 15:30:52,540 - INFO - Uvicorn server starting...
INFO:     Started server process [53131]
INFO:     Waiting for application startup.
[07/14/25 15:30:57] INFO     Running Neo4j Cypher MCP Server with  server.py:170
                             stdio transport...                                 
                    INFO     Processing request of type            server.py:625
                             ListToolsRequest                                   
INFO:     Application startup complete.
INFO:     Uvicorn running on http://0.0.0.0:8000 (Press CTRL+C to quit)

Actual Behavior

$ mcpo --config config.json
Starting MCP OpenAPI Proxy with config file: config.json
2025-07-14 15:10:15,420 - INFO - Starting MCPO Server...
2025-07-14 15:10:15,420 - INFO -   Name: MCP OpenAPI Proxy
2025-07-14 15:10:15,420 - INFO -   Version: 1.0
2025-07-14 15:10:15,420 - INFO -   Description: Automatically generated API from MCP Tool Schemas
2025-07-14 15:10:15,420 - INFO -   Hostname: XP43WG00FM
2025-07-14 15:10:15,420 - INFO -   Port: 8000
2025-07-14 15:10:15,420 - INFO -   API Key: Not Provided
2025-07-14 15:10:15,420 - INFO -   CORS Allowed Origins: ['*']
2025-07-14 15:10:15,420 - INFO -   Path Prefix: /
2025-07-14 15:10:15,420 - INFO - Loading MCP server configurations from: config.json
2025-07-14 15:10:15,422 - INFO - Configured MCP Servers:
2025-07-14 15:10:15,422 - INFO -   Configuring Stdio MCP Server 'time' with command: uvx with args: ['mcp-server-time', '--local-timezone=America/New_York']
2025-07-14 15:10:15,422 - INFO -   Configuring Stdio MCP Server 'neo4j-cypher' with command: uvx with args: ['mcp-neo4j-cypher', '--db-url', 'bolt://localhost:7687', '--username', 'neo4j', '--password', 'password123', '--namespace', 'lineage']
2025-07-14 15:10:15,422 - INFO - Uvicorn server starting...
INFO:     Started server process [45290]
INFO:     Waiting for application startup.
[07/14/25 15:10:19] INFO     Running Neo4j Cypher MCP Server with stdio transport...                                                                                              server.py:170
                    INFO     Processing request of type ListToolsRequest                                                                                                          server.py:625
ERROR:      + Exception Group Traceback (most recent call last):
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/starlette/routing.py", line 694, in lifespan
  |     async with self.lifespan_context(app) as maybe_state:
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/contextlib.py", line 210, in __aenter__
  |     return await anext(self.gen)
  |            ^^^^^^^^^^^^^^^^^^^^^
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 98, in lifespan
  |     async with AsyncExitStack() as stack:
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/contextlib.py", line 745, in __aexit__
  |     raise exc_details[1]
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/contextlib.py", line 728, in __aexit__
  |     cb_suppress = await cb(*exc_details)
  |                   ^^^^^^^^^^^^^^^^^^^^^^
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/contextlib.py", line 231, in __aexit__
  |     await self.gen.athrow(typ, value, traceback)
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 113, in lifespan
  |     async with stdio_client(server_params) as (reader, writer):
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/contextlib.py", line 231, in __aexit__
  |     await self.gen.athrow(typ, value, traceback)
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcp/client/stdio/__init__.py", line 180, in stdio_client
  |     async with (
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/anyio/_backends/_asyncio.py", line 772, in __aexit__
  |     raise BaseExceptionGroup(
  | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
    | Exception Group Traceback (most recent call last):
    |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcp/client/stdio/__init__.py", line 187, in stdio_client
    |     yield read_stream, write_stream
    |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 114, in lifespan
    |     async with ClientSession(reader, writer) as session:
    |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/anyio/_backends/_asyncio.py", line 772, in __aexit__
    |     raise BaseExceptionGroup(
    | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
    +-+---------------- 1 ----------------
      | Exception Group Traceback (most recent call last):
      |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 117, in lifespan
      |     yield
      |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 101, in lifespan
      |     await stack.enter_async_context(
      |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/contextlib.py", line 650, in enter_async_context
      |     result = await _enter(cm)
      |              ^^^^^^^^^^^^^^^^
      |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/contextlib.py", line 210, in __aenter__
      |     return await anext(self.gen)
      |            ^^^^^^^^^^^^^^^^^^^^^
      |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 113, in lifespan
      |     async with stdio_client(server_params) as (reader, writer):
      |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/contextlib.py", line 231, in __aexit__
      |     await self.gen.athrow(typ, value, traceback)
      |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcp/client/stdio/__init__.py", line 180, in stdio_client
      |     async with (
      |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/anyio/_backends/_asyncio.py", line 772, in __aexit__
      |     raise BaseExceptionGroup(
      | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
      +-+---------------- 1 ----------------
        | Exception Group Traceback (most recent call last):
        |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcp/client/stdio/__init__.py", line 187, in stdio_client
        |     yield read_stream, write_stream
        |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 114, in lifespan
        |     async with ClientSession(reader, writer) as session:
        |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/anyio/_backends/_asyncio.py", line 772, in __aexit__
        |     raise BaseExceptionGroup(
        | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
        +-+---------------- 1 ----------------
          | Traceback (most recent call last):
          |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 116, in lifespan
          |     await create_dynamic_endpoints(app, api_dependency=api_dependency)
          |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 61, in create_dynamic_endpoints
          |     response_model_fields = get_model_fields(
          |                             ^^^^^^^^^^^^^^^^^
          |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/utils/main.py", line 236, in get_model_fields
          |     python_type_hint, pydantic_field_info = _process_schema_property(
          |                                             ^^^^^^^^^^^^^^^^^^^^^^^^^
          |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/utils/main.py", line 204, in _process_schema_property
          |     item_type_hint, _ = _process_schema_property(
          |                         ^^^^^^^^^^^^^^^^^^^^^^^^^
          |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/utils/main.py", line 166, in _process_schema_property
          |     nested_type_hint, nested_pydantic_field = _process_schema_property(
          |                                               ^^^^^^^^^^^^^^^^^^^^^^^^^
          |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/utils/main.py", line 126, in _process_schema_property
          |     type_hint, _ = _process_schema_property(
          |                    ^^^^^^^^^^^^^^^^^^^^^^^^^
          |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/utils/main.py", line 112, in _process_schema_property
          |     assert ref in schema_defs, "Custom field not found"
          |            ^^^^^^^^^^^^^^^^^^
          | TypeError: argument of type 'NoneType' is not iterable
          +------------------------------------

ERROR:    Application startup failed. Exiting.

Steps to Reproduce

  1. create config.json
{
  "mcpServers": {
    "time": {
      "command": "uvx",
      "args": ["mcp-server-time", "--local-timezone=America/New_York"]
    },
    "neo4j-cypher": {
      "command": "uvx",
      "args": [
        "mcp-neo4j-cypher",
        "--db-url", "bolt://localhost:7687",
        "--username", "neo4j",
        "--password", "password123",
        "--namespace", "lineage"
      ]
    }
  }
}
  1. run uv run mcpo --config ./config.json

Logs & Screenshots

$ mcpo --config config.json
Starting MCP OpenAPI Proxy with config file: config.json
2025-07-14 15:10:15,420 - INFO - Starting MCPO Server...
2025-07-14 15:10:15,420 - INFO -   Name: MCP OpenAPI Proxy
2025-07-14 15:10:15,420 - INFO -   Version: 1.0
2025-07-14 15:10:15,420 - INFO -   Description: Automatically generated API from MCP Tool Schemas
2025-07-14 15:10:15,420 - INFO -   Hostname: XP43WG00FM
2025-07-14 15:10:15,420 - INFO -   Port: 8000
2025-07-14 15:10:15,420 - INFO -   API Key: Not Provided
2025-07-14 15:10:15,420 - INFO -   CORS Allowed Origins: ['*']
2025-07-14 15:10:15,420 - INFO -   Path Prefix: /
2025-07-14 15:10:15,420 - INFO - Loading MCP server configurations from: config.json
2025-07-14 15:10:15,422 - INFO - Configured MCP Servers:
2025-07-14 15:10:15,422 - INFO -   Configuring Stdio MCP Server 'time' with command: uvx with args: ['mcp-server-time', '--local-timezone=America/New_York']
2025-07-14 15:10:15,422 - INFO -   Configuring Stdio MCP Server 'neo4j-cypher' with command: uvx with args: ['mcp-neo4j-cypher', '--db-url', 'bolt://localhost:7687', '--username', 'neo4j', '--password', 'password123', '--namespace', 'lineage']
2025-07-14 15:10:15,422 - INFO - Uvicorn server starting...
INFO:     Started server process [45290]
INFO:     Waiting for application startup.
[07/14/25 15:10:19] INFO     Running Neo4j Cypher MCP Server with stdio transport...                                                                                              server.py:170
                    INFO     Processing request of type ListToolsRequest                                                                                                          server.py:625
ERROR:      + Exception Group Traceback (most recent call last):
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/starlette/routing.py", line 694, in lifespan
  |     async with self.lifespan_context(app) as maybe_state:
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/contextlib.py", line 210, in __aenter__
  |     return await anext(self.gen)
  |            ^^^^^^^^^^^^^^^^^^^^^
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 98, in lifespan
  |     async with AsyncExitStack() as stack:
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/contextlib.py", line 745, in __aexit__
  |     raise exc_details[1]
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/contextlib.py", line 728, in __aexit__
  |     cb_suppress = await cb(*exc_details)
  |                   ^^^^^^^^^^^^^^^^^^^^^^
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/contextlib.py", line 231, in __aexit__
  |     await self.gen.athrow(typ, value, traceback)
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 113, in lifespan
  |     async with stdio_client(server_params) as (reader, writer):
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/contextlib.py", line 231, in __aexit__
  |     await self.gen.athrow(typ, value, traceback)
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcp/client/stdio/__init__.py", line 180, in stdio_client
  |     async with (
  |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/anyio/_backends/_asyncio.py", line 772, in __aexit__
  |     raise BaseExceptionGroup(
  | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
    | Exception Group Traceback (most recent call last):
    |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcp/client/stdio/__init__.py", line 187, in stdio_client
    |     yield read_stream, write_stream
    |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 114, in lifespan
    |     async with ClientSession(reader, writer) as session:
    |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/anyio/_backends/_asyncio.py", line 772, in __aexit__
    |     raise BaseExceptionGroup(
    | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
    +-+---------------- 1 ----------------
      | Exception Group Traceback (most recent call last):
      |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 117, in lifespan
      |     yield
      |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 101, in lifespan
      |     await stack.enter_async_context(
      |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/contextlib.py", line 650, in enter_async_context
      |     result = await _enter(cm)
      |              ^^^^^^^^^^^^^^^^
      |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/contextlib.py", line 210, in __aenter__
      |     return await anext(self.gen)
      |            ^^^^^^^^^^^^^^^^^^^^^
      |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 113, in lifespan
      |     async with stdio_client(server_params) as (reader, writer):
      |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/contextlib.py", line 231, in __aexit__
      |     await self.gen.athrow(typ, value, traceback)
      |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcp/client/stdio/__init__.py", line 180, in stdio_client
      |     async with (
      |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/anyio/_backends/_asyncio.py", line 772, in __aexit__
      |     raise BaseExceptionGroup(
      | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
      +-+---------------- 1 ----------------
        | Exception Group Traceback (most recent call last):
        |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcp/client/stdio/__init__.py", line 187, in stdio_client
        |     yield read_stream, write_stream
        |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 114, in lifespan
        |     async with ClientSession(reader, writer) as session:
        |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/anyio/_backends/_asyncio.py", line 772, in __aexit__
        |     raise BaseExceptionGroup(
        | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
        +-+---------------- 1 ----------------
          | Traceback (most recent call last):
          |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 116, in lifespan
          |     await create_dynamic_endpoints(app, api_dependency=api_dependency)
          |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/main.py", line 61, in create_dynamic_endpoints
          |     response_model_fields = get_model_fields(
          |                             ^^^^^^^^^^^^^^^^^
          |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/utils/main.py", line 236, in get_model_fields
          |     python_type_hint, pydantic_field_info = _process_schema_property(
          |                                             ^^^^^^^^^^^^^^^^^^^^^^^^^
          |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/utils/main.py", line 204, in _process_schema_property
          |     item_type_hint, _ = _process_schema_property(
          |                         ^^^^^^^^^^^^^^^^^^^^^^^^^
          |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/utils/main.py", line 166, in _process_schema_property
          |     nested_type_hint, nested_pydantic_field = _process_schema_property(
          |                                               ^^^^^^^^^^^^^^^^^^^^^^^^^
          |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/utils/main.py", line 126, in _process_schema_property
          |     type_hint, _ = _process_schema_property(
          |                    ^^^^^^^^^^^^^^^^^^^^^^^^^
          |   File "/Users/yohei.onishi/.local/share/mise/installs/python/3.11.9/lib/python3.11/site-packages/mcpo/utils/main.py", line 112, in _process_schema_property
          |     assert ref in schema_defs, "Custom field not found"
          |            ^^^^^^^^^^^^^^^^^^
          | TypeError: argument of type 'NoneType' is not iterable
          +------------------------------------

ERROR:    Application startup failed. Exiting.

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