Created by: jmini
Fix this null pointer:
Exception in thread "main" java.lang.NullPointerException
at org.openapitools.codegen.DefaultGenerator.generateModels(DefaultGenerator.java:297)
at org.openapitools.codegen.DefaultGenerator.generate(DefaultGenerator.java:783)
When the generator is started on a OAS3 without any components section like ping.yaml
This PR also activate one test case that was ignored and add a new one.