Plugin is failing with endpoints and inlined parameters + additionalProperties

[cortinico]

Just got a bug report on Slack for swagger-gradle-codegen (credits to @vanniktech). After some small investigation with @macisamuele looks like the issue is with paths that have parameters with inlined additional properties.

Here a minimal spec that is breaking the plugin:

{
  "swagger": "2.0",
  "info": {
    "version": "1.0",
    "title": ""
  },
  "definitions": {
    "model": {
      "type": "object",
      "additionalProperties": {
        "type": "string"
      }
    }
  },
  "paths": {
    "/works": {
      "post": {
        "parameters": [
          {
            "in": "body",
            "name": "body",
            "schema": {
              "$ref" : "#/definitions/model"
            }
          }
        ],
        "responses": {
          "default": {
            "description": "something"
          }
        }
      }
    },
    "/broken": {
      "post": {
        "parameters": [
          {
            "in": "body",
            "name": "body",
            "schema": {
              "type": "object",
              "additionalProperties": {
                "type": "string"
              }
            }
          }
        ],
        "responses": {
          "default": {
            "description": "something"
          }
        }
      }
    }
  }
}

The current workaround is to replace this:

         {
            "in": "body",
            "name": "body",
            "schema": {
              "type": "object",
              "additionalProperties": {
                "type": "string"
              }
            }
          }

with:

          {
            "in": "body",
            "name": "body",
            "schema": {
              "$ref" : "#/definitions/model"
            }
          }

And have the additionalProperties not defined inline.

Here the failure message:

Execution failed for task ':generateSwagger'.
> Could not process operation:
    Tag: Tag {
  	name: default
  	description: null
  	externalDocs: null
  	extensions:{}}
    Operation: null
    Resource: post /broken
    Definitions: {model=io.swagger.models.ModelImpl@a2a8ef}
    Exception: null cannot be cast to non-null type io.swagger.models.ModelImpl