[BUG][typescript-axios] Broken client

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?

Description

openapi-generator create broken client for attached schema.
Errors:

• Types error:

  > 75 |         apiProblemCreate: async (tags: Array<ProblemTagRequest>, options: any = {}): Promise<RequestArgs> => {
       |                                              ^ // ProblemTagRequest does not exist
    76 |             // verify required parameter 'tags' is not null or undefined
    77 |             assertParamExists('apiProblemCreate', 'tags', tags)
    78 |             const localVarPath = `/api/problem/`;

• DataForm usage error

92 |  localVarFormParams.append(tags.join(COLLECTION_FORMATS.csv));
                               ^ // here should be append('tags', tags...

• wrong array usage

92 |    localVarFormParams.append(tags.join(COLLECTION_FORMATS.csv));
                                         ^ // join returns [object Object],[object Object],

openapi-generator version

5.0.1
latest dev version

OpenAPI declaration schema

https://gist.github.com/vmstarchenko/9671d45499a66d73b6746e69168c6cc5

Generation Details

java -jar ./openapi-generator-5.0.1/modules/openapi-generator-cli/target/openapi-generator-cli.jar generate -i ./api-spec.yaml -g typescript-axios --additional-properties=useSingleRequestParameter=true -o ./client/typescript-axios

Generated client:
https://gist.github.com/vmstarchenko/5128a715559fcb065649b37b316f3be9

Steps to reproduce

Generate typescript-axios client with useSingleRequestParameter additional property and attached schema

Related issues/PRs

Suggest a fix

Start by running the documented openapi-generator CLI command with api-spec.yaml and the typescript-axios generator, then inspect the generated client linked in the report. The fix is complete when the generated client defines ProblemTagRequest, uses the expected form field name, and serializes the array values correctly.