Several python-nss functions/methods state they can read their input from either a string or any file like object (e.g. PKCS12Decoder). There is a bug in the common routine used to read the data for these entry points. It only worked for strings and file objects (or derived from the file object class). It fails to work for file like objects that implement the file interface (e.g. StringIO).
python-nss-0.16.0-1.fc22 has been submitted as an update for Fedora 22. https://admin.fedoraproject.org/updates/python-nss-0.16.0-1.fc22
Package python-nss-0.16.0-1.fc22: * should fix your issue, * was pushed to the Fedora 22 testing repository, * should be available at your local mirror within two days. Update it with: # su -c 'yum update --enablerepo=updates-testing python-nss-0.16.0-1.fc22' as soon as you are able to. Please go to the following url: https://admin.fedoraproject.org/updates/FEDORA-2015-8995/python-nss-0.16.0-1.fc22 then log in and leave karma (feedback).
python-nss-0.16.0-1.fc22 has been pushed to the Fedora 22 stable repository. If problems still persist, please make note of it in this bug report.