Do not add an extra empty entry to read-only parallel list fields

6 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

00:44:42

passed ERP5.PerformanceTest-Master

00:25:52

failed ERP5.UnitTest-Master

01:20:14

failed ERP5.UnitTest-Master.Medusa

01:18:35

passed SlapOS.Eggs.UnitTest-Master.Python2

00:53:36

passed SlapOS.Eggs.UnitTest-Master.Python3

00:12:38