NPE at ModelImpl

Hi

I currently facing this stack trace

java.lang.RuntimeException: Could not process operation:
  Tag: AssetGroups
  Operation: addAssets
  Resource: put /api/v2/assetGroups/{id}/assetList
  Definitions: {Addresses=io.swagger.models.ModelImpl@9901aa0, 
AppHost=io.swagger.models.ModelImpl@8456d641, ....
  Exception: null
        at io.swagger.codegen.DefaultGenerator.processOperation(DefaultGenerator.java:861)
        at io.swagger.codegen.DefaultGenerator.processPaths(DefaultGenerator.java:763)
       at io.swagger.codegen.DefaultGenerator.generateApis(DefaultGenerator.java:388)
       at io.swagger.codegen.DefaultGenerator.generate(DefaultGenerator.java:700)

after upgrading from swagger-codegen-maven-plugin 2.2.2 to 2.2.3 where I generate java source from swagger spec

Need suggestion on how to look for abnormalities in my swagger spec file which can cause this issue ( or this can just be regression )

Thanks

Swagger-codegen version

2.2.3

Start with DefaultGenerator.java at processOperation, processPaths, and generateApis, then compare behavior between swagger-codegen 2.2.2 and 2.2.3 using the reported AssetGroups/addAssets operation. Inspect the Swagger definitions and operation details for the condition that produces the null exception; done means identifying a reproducible spec or regression and documenting the finding or a focused fix path.