[Bug]Exception in OpenAPI Normalizer - maybe related to handling anyOf

[newsgrep]

Description

It seems like there is a problem with anyOf in the contect of response's. When I try to generate my API I get an exception. Excerpt of the OpenAPI file: myapi.json
From Version 7.6

[main] ERROR o.o.codegen.DefaultGenerator - An exception occurred in OpenAPI Normalizer. Please report the issue via https://github.com/openapitools/openapi-generator/issues/new/:
[main] ERROR o.o.codegen.DefaultGenerator - An exception occurred in OpenAPI Normalizer. Please report the issue via https://github.com/openapitools/openapi-generator/issues/new/: 
java.util.NoSuchElementException
        at java.base/java.util.LinkedHashMap$LinkedHashIterator.nextNode(LinkedHashMap.java:758)
        at java.base/java.util.LinkedHashMap$LinkedKeyIterator.next(LinkedHashMap.java:778)
        at org.openapitools.codegen.utils.ModelUtils.getType(ModelUtils.java:2141)
        at org.openapitools.codegen.utils.ModelUtils.isArraySchema(ModelUtils.java:594)
        at org.openapitools.codegen.OpenAPINormalizer.normalizeSchema(OpenAPINormalizer.java:512)
        at org.openapitools.codegen.OpenAPINormalizer.normalizeAnyOf(OpenAPINormalizer.java:659)
        at org.openapitools.codegen.OpenAPINormalizer.normalizeSchema(OpenAPINormalizer.java:522)
        at org.openapitools.codegen.OpenAPINormalizer.normalizeContent(OpenAPINormalizer.java:367)
        at org.openapitools.codegen.OpenAPINormalizer.normalizeResponses(OpenAPINormalizer.java:438)
        at org.openapitools.codegen.OpenAPINormalizer.normalizePaths(OpenAPINormalizer.java:330)
        at org.openapitools.codegen.OpenAPINormalizer.normalize(OpenAPINormalizer.java:286)
        at org.openapitools.codegen.DefaultGenerator.configureGeneratorProperties(DefaultGenerator.java:279)
        at org.openapitools.codegen.DefaultGenerator.generate(DefaultGenerator.java:1289)
        at org.openapitools.codegen.cmd.Generate.execute(Generate.java:535)
	at org.openapitools.codegen.cmd.OpenApiGeneratorCommand.run(OpenApiGeneratorCommand.java:32)
	at org.openapitools.codegen.OpenAPIGenerator.main(OpenAPIGenerator.java:66)
Exception in thread "main" java.util.NoSuchElementException
	at java.base/java.util.LinkedHashMap$LinkedHashIterator.nextNode(LinkedHashMap.java:758)
	at java.base/java.util.LinkedHashMap$LinkedKeyIterator.next(LinkedHashMap.java:778)
	at org.openapitools.codegen.utils.ModelUtils.getType(ModelUtils.java:2141)
	at org.openapitools.codegen.utils.ModelUtils.isArraySchema(ModelUtils.java:594)
	at org.openapitools.codegen.InlineModelResolver.gatherInlineModels(InlineModelResolver.java:341)
	at org.openapitools.codegen.InlineModelResolver.gatherInlineModels(InlineModelResolver.java:407)
	at org.openapitools.codegen.InlineModelResolver.flattenContent(InlineModelResolver.java:471)
	at org.openapitools.codegen.InlineModelResolver.flattenResponses(InlineModelResolver.java:555)
	at org.openapitools.codegen.InlineModelResolver.flattenPaths(InlineModelResolver.java:149)
	at org.openapitools.codegen.InlineModelResolver.flatten(InlineModelResolver.java:108)
	at org.openapitools.codegen.DefaultGenerator.configureGeneratorProperties(DefaultGenerator.java:292)
	at org.openapitools.codegen.DefaultGenerator.generate(DefaultGenerator.java:1289)
	at org.openapitools.codegen.cmd.Generate.execute(Generate.java:535)
	at org.openapitools.codegen.cmd.OpenApiGeneratorCommand.run(OpenApiGeneratorCommand.java:32)
	at org.openapitools.codegen.OpenAPIGenerator.main(OpenAPIGenerator.java:66)

openapi-generator version

Get the same error 7.6 and 7.7-Snapshot
But not on 7.4 and 7.5

OpenAPI declaration file content or url

myapi.json

Command line used for generation

openapi-generator-cli generate -g java -i myapi.json
running Fedora Linux

Steps to reproduce

run any generator with the attached myapi.json

Related issues/PRs

#18655
#18732

Suggest a fix/enhancement

Please add a more descriptive exception for similar issues.

[wing328]

should be fixed via #19014

please give it a try with the latest master (snapshot version mentioned in the project's readme will be published later as part of the travis ci workflow)