Swagger codegen RX JAVA + Retrofit not working

I tried to export RX JAVA + Retrofit client from swagger hub , by entering Codegen Options and enabling check box of (useRxJava2) in the java client , however when i export the java client it does not work as expected and the code doesn't have neither retrofit nor rx java ! (uses oktthp only)

Also i tried to download the json file from swagger hub (Export -> Download Api) and followed the steps here

RX JAVA + Retrofit sdk generation using Swagger codegen

But when i run the command , i get this in the command line :

[main] INFO io.swagger.parser.Swagger20Parser - reading from openapi.json
[main] INFO io.swagger.parser.Swagger20Parser - reading from openapi.json
[main] INFO io.swagger.codegen.ignore.CodegenIgnoreProcessor - No .swagger-codeg
en-ignore file found.
Exception in thread "main" java.lang.RuntimeException: missing swagger input or
config!
        at io.swagger.codegen.DefaultGenerator.generate(DefaultGenerator.java:13
2)
        at io.swagger.codegen.cmd.Generate.run(Generate.java:223)
        at io.swagger.codegen.SwaggerCodegen.main(SwaggerCodegen.java:36)

Any clue how can i bypass this ?

Start with the generation command that reads openapi.json and the DefaultGenerator.generate and Generate.run entries shown in the stack trace. Verify how the input and config arguments are supplied, then confirm that generation produces a Java client using Retrofit and RxJava2 rather than only OkHttp, without the missing-input/config failure.