GAE endpoints problem with integers

app.yaml

application: your-app-id
version: 1
runtime: python27
threadsafe: true
api_version: 1

# Handlers tell App Engine how to route requests to your application.
handlers:

# This handler routes requests to your APIs to your Endpoints code.
# See https://developers.google.com/appengine/docs/python/endpoints/
- url: /_ah/spi/.*
  script: example.app
  secure: always

libraries:
- name: endpoints
  version: 1.0

example.py

import endpoints
from protorpc import messages
from protorpc import message_types
from protorpc import remote

package = 'Example'

class Number(messages.Message):
    number = messages.IntegerField(1)

@endpoints.api(name='example', version='v1')
class ExampleApi(remote.Service):
    @endpoints.method(message_types.VoidMessage, Number,
            path = "getNumber", http_method='GET', name = 'getNumber')
    def get_number(self, _):
        return Number(number = 123)  # This is an integer. Isn't?

app = endpoints.api_server([ExampleApi])

question.md

When the API endpoint is invoked via the API explorer, or simply via:

$ curl http://localhost:8080//_ah/api/example/v1/getNumber

The following JSON is received

{
 "number": "123"
}

Why is "123" a string? Since the message type was declared as IntegerField() I expected it to be an integer instead, i.e. I expected the following JSON:

{
 "number": 123
}

Setting the variant to a 32 bit integer type fixes the issue.

class Number(messages.Message):
    number = messages.IntegerField(1, variant=messages.Variant.INT32)