Add check to exclude empty strings

Former-commit-id: 99bbb242
Former-commit-id: f2779617

steps/identify_bad_antennas_join.cwl

@@ -31,6 +31,7 @@ arguments:
     flagged_antenna_list = set.intersection(*map(set, flaggedants_list))
 
     for flagged_antenna in flagged_antenna_list:
+        if flagged_antenna != '':
             filter += ';!' + flagged_antenna + '*&&*'
 
     cwl_output  = {"filter": filter}