[python-flask] invalid content of a generated `__init__.py` file

Hello,

Checklist from your CONTRIBUTING files :

• I have not found a matching issue, neither in swagger-api/swagger-codegen nor swagger-codegen-generators
• I am using the latest master
  • kinda, I'm using the Docker version of 2 weeks ago : swaggerapi/swagger-codegen-cli-v3:3.0.54
• test locally with the most recent jar
  • I'll try to do it soon

Using the python-flask generator, I sometimes find myself with invalid __init__.py files, containing four NULL (0x00) bytes. When Python then tries to parse them, it fails (and thus the server does not start).

Minimal reproducible example :

openapi.yml

openapi: 3.0.3
info:
  title: Minimal Reproducible Example
  description: "."
  version: 0.0.0
paths:
  /foo:
    get:
      summary: Get
      responses:
        "200":
          description: Status details
      operationId: foo_123

generate_server.bash

set -euo pipefail  # check for errors

echo '(re-)create output directory'
rm -Rf ./output && mkdir ./output
echo 'copy the OpenAPI file into it'
cp ./openapi.yml ./output
echo 'generate the server files from the OpenAPI file'
docker run \
    --rm \
    -u "$(id -u):$(id -g)" \
    -v "${PWD}/output:/local" \
    swaggerapi/swagger-codegen-cli-v3:3.0.54 \
    generate \
    -l python-flask \
    -i /local/openapi.yml \
    -o /local
echo 'check the content of one of the generated __init__.py files'
hexdump -C ./output/swagger_server/controllers/__init__.py

It produces :

check the content of one of the generated __init__.py files
00000000  00 00 00 00                                       |....|
00000004

(if you are not familiar with hexdump, it prints the binary content of a file)
Here we can see that the file contains four 0x00 (NULL) bytes. This is not a valid Python file.

I don't know what causes it.

Expected content : empty (0 bytes), or valid Python content (like in some other generated __init__.py files)

Actual content : four NULL (0x00) bytes.

Reproduce the issue with openapi.yml, generate_server.bash, and the swaggerapi/swagger-codegen-cli-v3:3.0.54 Docker image, then inspect the generated swagger_server/controllers/init.py file. Trace the python-flask generator templates or generation path that produces this file; done means generated init.py files are empty or valid Python without NULL bytes.