[Python] Query parameter sent as "None" when it is passed as None

Description

When the query parameter is optional, if the parameter is passed as None it is sent as the string None

Swagger-codegen version

2.4.8

Swagger declaration file content or url

/pets:
    get:
      summary: List all pets
      operationId: listPets
      tags:
        - pets
      parameters:
        - name: limit
          in: query
          description: How many items to return at one time (max 100)
          required: false
          schema:
            type: integer
            format: int32

Command line used for generation

swagger-codegen generate -i http://petstore.swagger.io/v2/swagger.json -l python -o /tmp/test/

Steps to reproduce

Pass limit as None in get pets API. The limit is passed as host.com/pets?limit=None

Related issues/PRs

Did not find any

Suggest a fix/enhancement

When an optional query param is None, do not pass the value as 'None' rather don't pass the variable

Start with the generated Python client's handling of optional query parameters and reproduce the /pets request with limit=None. Trace how that value is serialized; done means an unset optional parameter is omitted rather than sent as limit=None. The issue names no source file or test to begin with.