[BUG] Incompatible Content type handling leading to NPE

[prezmer]

Version 5.2.1 generated Java class ApiClient which contained method

    public String selectHeaderContentType(String[] contentTypes) {
        if (contentTypes.length == 0 || contentTypes[0].equals("*/*")) {
            **return "application/json";**
        }
        for (String contentType : contentTypes) {
            if (isJsonMime(contentType)) {
                return contentType;
            }
        }
        return contentTypes[0];
    }

Version 5.3.x (0 and 1) generates modified body of the method

    public String selectHeaderContentType(String[] contentTypes) {
        if (contentTypes.length == 0) {
            **return null;**
        }

        if (contentTypes[0].equals("*/*")) {
            return "application/json";
        }

        for (String contentType : contentTypes) {
            if (isJsonMime(contentType)) {
                return contentType;
            }
        }

        return contentTypes[0];
    }

Returning null when argument is empty finally causes NPE in existing code. I guess that we should avoid returning as a rule of clean code.

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?
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Description

NPE thrown in a java client code

openapi-generator version

5.3.x
5.2.x works fine

Suggest a fix

instead of
if (contentTypes.length == 0) {
return null;
}

use
if (contentTypes.length == 0) {
return "application/json";
}

[wing328]

@prezmer thanks for reporting the issue. Can you please provide a spec to reproduce the issue?

[aranjan99]

I face a similar issue, the java sdk generated with version 5.3.x adds a Content-Type header to get/delete requests. The value for this header field is empty and hence when the API call is made it fails with 400 error. I have to either manually exclude null/empty headers or change content-type to pass application/json instead of null

[JannikScholz]

This seems to have already been fixed in #11315 which isn't released yet.