[BUG][swift5] Closure isn't called anymore in latest snapshot with default configuration

Created by: fl034

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?
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Description

This project showcases a weird error where callback closure is not called.

This happens with the default library selected (URLSession). With Alamofire, everything is fine.
In the 5.0.0 stable version, the error is not happening
Snapshot Commit: 90ed1290 from 2020-01-22
Tested with Xcode 12.3 (12C33) on macOS Catalina 10.15.7 (19H15)
Try switching the generator from snapshot to stable pod in Podfile to see the change.

openapi-generator version

5.0.1-snapshot (commit 90ed1290)

OpenAPI declaration file content or url

See test-project: https://github.com/fl034/Test-OAS

Generation Details

Swift5 with defaults

Steps to reproduce

Run sample project

Related issues/PRs

Nothing found

Suggest a fix

The issue seems to be in URLSessionImplementations.swift in line 137. self seems to be deallocated immediately, because it’s weak.
When I remove [weak self] it works again. But this isn’t the root of the problem, since the stable version also has [weak self]