BUG: An unhandled exception after printing the result

[mfarahy]

After printing results I receive this error:

`--------------------------------------------------------------------------
-- Result --

               API changes are backward compatible                    

---

Unexpected exception. Reason: Cannot invoke "org.openapitools.openapidiff.core.model.ChangedSchema.isIncompatible()" because "schema" is null
java.lang.NullPointerException: Cannot invoke "org.openapitools.openapidiff.core.model.ChangedSchema.isIncompatible()" because "schema" is null
at org.openapitools.openapidiff.core.output.HtmlRender.div_changedSchema(HtmlRender.java:358)
at org.openapitools.openapidiff.core.output.HtmlRender.li_changedRequest(HtmlRender.java:346)
at org.openapitools.openapidiff.core.output.HtmlRender.ul_request(HtmlRender.java:330)
at org.openapitools.openapidiff.core.output.HtmlRender.ol_changed(HtmlRender.java:212)
at org.openapitools.openapidiff.core.output.HtmlRender.render(HtmlRender.java:106)
at org.openapitools.openapidiff.cli.Main.main(Main.java:245)
⚠️ API changes broke backward compatibility`