[PYTHON] Content-Type should not be forced added to all requests

Description

Generated python client seems to add Conten-Type: application/json to all requests, even though I don't have specify any content-type in the swagger declaration. This cause a problem to my server, because a GET request should not have Content-Type in the header.

Swagger-codegen version

3.0.36 (from Maven.org)

Swagger declaration file content or url

JSON file here

Command line used for generation

java -jar swagger-codegen-cli.jar generate -i building_resource_spec.json -o ./output_building -l python

Steps to reproduce

After the python clients are generated, check output_building/swagger_client/rest.py line 149. You can see that, the Content-Type is added to all requests.

        if 'Content-Type' not in headers:
            headers['Content-Type'] = 'application/json'

Suggest a fix/enhancement

I would expect at least that, the Content-Type is only added to PUT and PATCH requests

Reproduce the generation command and inspect output_building/swagger_client/rest.py at line 149, where Content-Type is added. Trace that generated code back to its Python client template and verify that the resulting client does not add Content-Type to GET requests when the Swagger declaration does not specify it.