title: Swagger codegen failed: missing swagger input or config
body: <p>I have <a href="https://gist.github.com/sagunji/9a7a39c102d5638bfb557314d2237a37#file-api-docs-json" rel="noreferrer">this json file</a> and I have been trying to create models and API code through swagger codegen. This has not been quiet effective as it throws error.</p>
  
  <pre><code>Exception in thread "main" java.lang.RuntimeException: missing swagger input or config!
      at io.swagger.codegen.DefaultGenerator.generate(DefaultGenerator.java:735)
      at io.swagger.codegen.cmd.Generate.run(Generate.java:285)
      at io.swagger.codegen.SwaggerCodegen.main(SwaggerCodegen.java:35)
  </code></pre>
  
  <p>The swagger docs version is 1.2. And I am using swagger-codegen version 2.4.0. </p>
  
  <pre><code>java -jar modules\swagger-codegen-cli\target\swagger-codegen-cli.jar generate -i ./json/docs.json -l python -o C:/Users/sk/projects/generated-sdk
  </code></pre>