This issue relates to JENKINS-30018

Two things:
1) In our case someone added third regular expression input field to Pipelines section, left it completely empty and saved the configuration. As a result our jenkins.log started to grow rapidly.

Aug 18, 2015 10:42:38 AM se.diabol.jenkins.pipeline.util.ProjectUtil getProjects
WARNING: Could not find match group

Above output 1223 times per second and now our jenkins.log is counted in tens of gigs. The spamming stopped when the empty field was removed.

It should not be possible to leave regular expression input field blank, but it should be removed when view configuration is saved.

2) Is it really necessary call getProjects function that often?