Failure to collect RPM from RPM db in scancode.io

This is a problem that came from running the toolkit on a Docker image https://hub.docker.com/r/ansible/awx_web/tags
docker.io/ansible/awx_web:1.0.6 :
```
stat: path should be string, bytes, os.PathLike or integer, not NoneType

Traceback:
File "/opt/scancodeio/scanpipe/pipelines/__init__.py", line 95, in execute
step(self)
File "/opt/scancodeio/scanpipe/pipelines/docker.py", line 79, in collect_and_create_system_packages
docker.scan_image_for_system_packages(self.project, image)
File "/opt/scancodeio/scanpipe/pipes/docker.py", line 123, in scan_image_for_system_packages
for i, (purl, package, layer) in enumerate(installed_packages):
File "/usr/local/lib/python3.9/site-packages/container_inspector/image.py", line 329, in get_installed_packages
for purl, package in layer.get_installed_packages(packages_getter):
File "/opt/scancodeio/scanpipe/pipes/rpm.py", line 31, in package_getter
for package in packages:
File "/usr/local/lib/python3.9/site-packages/packagedcode/rpm_installed.py", line 43, in parse_rpm_xmlish
if not os.path.exists(location):
File "/usr/local/lib/python3.9/genericpath.py", line 19, in exists
os.stat(path)
```