system: You are an expert security code reviewer. You will be shown a source code file along with a multiple-choice question listing several function or class names from that file. Your task is to identify which one contains the specified CWE vulnerability.

OUTPUT FORMAT: Respond with the single letter of the correct option, wrapped in \boxed{...}. Example: `\boxed{B}`. Output the boxed letter ONLY -- no explanation, no other text.

user: ```python
from datetime import datetime, timedelta
import logging
import time
from typing import Tuple

import flask
from typing import List, Optional

from implicitdict import ImplicitDict
from . import webapp, basic_auth
from .database import db, Query, QueryState


logging.basicConfig()
_logger = logging.getLogger('atproxy.handler')
_logger.setLevel(logging.DEBUG)


class PendingRequest(ImplicitDict):
    """A pending query the handler client is expected to handle."""

    id: str
    """ID of the query; used to PUT /handler/queries/<id> the result."""

    type: str
    """Type of query -- matches a request_type_name() in requests.py."""

    request: dict
    """All relevant information about the request in the *Request descriptor from requests.py matching `type`."""


class ListQueriesResponse(ImplicitDict):
    """Response body schema for GET /handler/queries."""

    requests: List[PendingRequest]
    """All of the queries available for the handler client to handle."""


class PutQueryRequest(ImplicitDict):
    """Request body schema for PUT /handler/queries/<id>."""

    response: Optional[dict] = None
    """JSON body of the response, or None for no JSON body."""

    return_code: int
    """HTTP return code."""


@webapp.route('/handler/queries', methods=['GET'])
@basic_auth.login_required
def list_queries() -> Tuple[str, int]:
    """Lists outstanding queries to be handled.

    See ListQueriesResponse for response body schema.
    """
    t_start = datetime.utcnow()
    _logger.debug('Handler requesting queries')
    max_timeout = timedelta(seconds=5)
    while datetime.utcnow() < t_start + max_timeout:
        with db as tx:
            response = ListQueriesResponse(requests=[
                PendingRequest(id=id, type=q.type, request=q.request)
                for id, q in tx.queries.items()
                if q.state == QueryState.Queued])
            if response.requests:
                _logger.debug('Provided handler {} queries'.format(len(response.requests)))
                return flask.jsonify(response)
        time.sleep(0.1)
    _logger.debug('No queries available for handler')
    return flask.jsonify(ListQueriesResponse(requests=[]))


@webapp.route('/handler/queries/<id>', methods=['PUT'])
@basic_auth.login_required
def put_query_result(id: str) -> Tuple[str, int]:
    """Fulfills an outstanding query.

    See PutQueryRequest for request body schema.
    """
    try:
        request: PutQueryRequest = ImplicitDict.parse(flask.request.json, PutQueryRequest)
    except ValueError as e:
        return flask.jsonify({'message': 'Could not parse PutQueryRequest: {}'.format(e)}), 400
    with db as tx:
        if id not in tx.queries:
            return flask.jsonify({'message': 'No outstanding request with ID {} exists'.format(id)}), 400
        query: Query = tx.queries[id]
        _logger.debug('{} query {} handled with code {}'.format(query.type, id, request.return_code))
        query.return_code = request.return_code
        query.response = request.response
        query.state = QueryState.Complete
    return '', 204

```

Which of the following functions or classes contains a `CWE-209: Generation of Error Message Containing Sensitive Information` vulnerability?

  A) ListQueriesResponse
  B) PendingRequest
  C) PutQueryRequest
  D) put_query_result
Answer: D