I configured Crowd2 authentication successfully and saved jenkins.yaml. Then I tried loading that file back (with minor changes to load passwords from files). Jenkins crashed, the logs indicated that the crash happened in CrowdSecurityRealm.java, line 203. In crowd2-plugin version 3.1.2 that line is:

this.group = group.trim();

There was no "group" field in jenkins.yaml. Once I added

group: ""

under jenkins/securityRealm/crowd, the config loading started working.

Please make the code robust to the case when "group" is empty, e.g. convert null to an empty string.