[BUG][Elm] Generation crashes with Exception: Property type is missing from getVars

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?

• Using the full Stripe API spec.

• Have you validated the input using an OpenAPI validator (example)?

• I used the CLI with validate and it found no issues.

• Have you tested with the latest master to confirm the issue still exists?

• Yes

• Have you searched for related issues/PRs?
• What's the actual output vs expected output?

Description

The elm generator produces partial output and broken code before failing with this error:

  Exception: Property type is missing from getVars
	at org.openapitools.codegen.DefaultGenerator.processOperation(DefaultGenerator.java:1187)
	at org.openapitools.codegen.DefaultGenerator.processPaths(DefaultGenerator.java:1078)
	at org.openapitools.codegen.DefaultGenerator.generateApis(DefaultGenerator.java:580)
	at org.openapitools.codegen.DefaultGenerator.generate(DefaultGenerator.java:915)
	at org.openapitools.codegen.cmd.Generate.execute(Generate.java:465)
	at org.openapitools.codegen.cmd.OpenApiGeneratorCommand.run(OpenApiGeneratorCommand.java:32)
	at org.openapitools.codegen.OpenAPIGenerator.main(OpenAPIGenerator.java:66)
Caused by: java.lang.RuntimeException: Property type is missing from getVars
	at org.openapitools.codegen.DefaultCodegen.addRequiredVarsMap(DefaultCodegen.java:7319)
	at org.openapitools.codegen.DefaultCodegen.addVarsRequiredVarsAdditionalProps(DefaultCodegen.java:7354)
	at org.openapitools.codegen.DefaultCodegen.fromParameter(DefaultCodegen.java:4972)
	at org.openapitools.codegen.DefaultCodegen.fromOperation(DefaultCodegen.java:4394)
	at org.openapitools.codegen.DefaultGenerator.processOperation(DefaultGenerator.java:1155)
	... 6 more

openapi-generator version

6.2.0 (latest via npm)

OpenAPI declaration file content or url

https://raw.githubusercontent.com/stripe/openapi/master/openapi/spec3.json

Generation Details

Steps to reproduce

1. generate -i "https://raw.githubusercontent.com/stripe/openapi/master/openapi/spec3.json" -g elm -o elmStripeAPI

Reproduce the failure with the Stripe spec and the generate -i ... -g elm command. Start at DefaultGenerator.processOperation and trace through DefaultCodegen.fromParameter, addRequiredVarsMap, and addVarsRequiredVarsAdditionalProps; done means generation completes without the missing-property exception and produces valid Elm output.