Failed to run DebianOvalImprover improver ( TypeError: 'NoneType' object is not subscriptable)

```
Traceback (most recent call last):
File "/home/ziad/PycharmProjects/vulnerablecode/vulnerabilities/management/commands/improve.py", line 59, in improve_data
ImproveRunner(improver).run()
File "/home/ziad/PycharmProjects/vulnerablecode/vulnerabilities/improve_runner.py", line 47, in run
process_inferences(
File "/usr/lib/python3.10/contextlib.py", line 79, in inner
return func(*args, **kwds)
File "/home/ziad/PycharmProjects/vulnerablecode/vulnerabilities/improve_runner.py", line 71, in process_inferences
for inference in inferences:
File "/home/ziad/PycharmProjects/vulnerablecode/vulnerabilities/improvers/valid_versions.py", line 174, in get_inferences
valid_versions = self.get_package_versions(
File "/home/ziad/PycharmProjects/vulnerablecode/vulnerabilities/improvers/valid_versions.py", line 90, in get_package_versions
return versions_fetcher.get_until(package_name=api_name, until=until).valid_versions
File "/home/ziad/PycharmProjects/vulnerablecode/vulnerabilities/package_managers.py", line 101, in get_until
for version in self.fetch(package_name):
File "/home/ziad/PycharmProjects/vulnerablecode/vulnerabilities/package_managers.py", line 299, in fetch
for release in response["versions"]:
TypeError: 'NoneType' object is not subscriptable
Failed to run improver vulnerabilities.improvers.valid_versions.DebianOvalImprover. Continuing...

```