diff --git a/steps/identify_bad_antennas_join.cwl b/steps/identify_bad_antennas_join.cwl
index 03a3c2e5b9b6548c9325bbd9eaf18fcd96b5c514..8d2abd592872fa258946b480e05cdcd4e1b57481 100644
--- a/steps/identify_bad_antennas_join.cwl
+++ b/steps/identify_bad_antennas_join.cwl
@@ -14,30 +14,31 @@ inputs:
       type: string?
       default: '*&'
       doc: Filter these baselines for the comparison
-      
+
 label: identifyBadAntennas_join
 arguments:
   - '-c'
   - |
-  
+
     import sys
     import json
-    
+
     flaggedants = $(inputs.flaggedants)
     filter = '$(inputs.filter)'
 
-    
+
     flaggedants_list = [ flaggedant.split(',') for flaggedant in flaggedants ]
-    flagged_antenna_list = set.intersection(*map(set, flaggedants_list)) 
+    flagged_antenna_list = set.intersection(*map(set, flaggedants_list))
 
     for flagged_antenna in flagged_antenna_list:
-        filter += ';!' + flagged_antenna + '*&&*'
+        if flagged_antenna != '':
+            filter += ';!' + flagged_antenna + '*&&*'
 
     cwl_output  = {"filter": filter}
 
     with open('./out.json', 'w') as fp:
         json.dump(cwl_output, fp)
-        
+
 outputs:
   - id: filter_out
     type: string
@@ -48,10 +49,10 @@ outputs:
   - id: logfile
     type: File?
     outputBinding:
-      glob: identifyBadAntennas.log    
-        
+      glob: identifyBadAntennas.log
+
 requirements:
   - class: InlineJavascriptRequirement
 
 stdout: identifyBadAntennas.log
-stderr: identifyBadAntennas_err.log
\ No newline at end of file
+stderr: identifyBadAntennas_err.log