[Spring] Query params using content: generate invalid code

Description

Using content instead of schema for query param generates code omitting the parameter & type of the query param in the Spring controller.

See schema versus content in https://swagger.io/docs/specification/describing-parameters/#query-parameters

The swagger definition below generates the following list() operation. The parameter annotations are there but no parameter name or type.

    public ResponseEntity<String> list(@ApiParam(value = "") @Valid @RequestParam(value = "filter", required = false)  ) {
        String accept = request.getHeader("Accept");
        return new ResponseEntity<String>(HttpStatus.NOT_IMPLEMENTED);
    }

Swagger-codegen version

3.0.8

Swagger declaration file content or url

openapi: 3.0.1
info:
  title: query param content
  version: 1.0

paths:

  /test:
    get:
      operationId: list
      parameters:
        # See schema versus content.  https://swagger.io/docs/specification/describing-parameters/#query-parameters
        - in: query
          name: filter
          # Wrap 'schema' into 'content.<media-type>'
          content:
            application/json:  # <---- media type indicates how to serialize / deserialize the parameter content
              schema:
                type: object
                properties:
                  type:
                    type: string
                  color:
                    type: string

      responses:
        200:
          description: successful operation
          content:
            application/json:
              schema:
                type: string

Command line used for generation

swagger-codegen generate -i query-param-content.yaml -o output --lang spring

Steps to reproduce

Save swagger above in query-param-content.yaml and run the codegen line above.

Related issues/PRs

Suggest a fix/enhancement

Reproduce the issue with query-param-content.yaml and the documented swagger-codegen generate command using --lang spring. Start at the Spring generator entry point and its templates, then verify that the generated list() operation includes the query parameter's name and type instead of an incomplete declaration.