--- a/qiime2/qiime_demux_emp-single.xml	Wed Jul 17 01:53:11 2019 -0400
+++ b/qiime2/qiime_demux_emp-single.xml	Tue Aug 13 07:40:25 2019 -0400
@@ -11,6 +11,7 @@
 --m-barcodes-column="$mbarcodescolumn"
 
 
+#if $input_files_mbarcodesfile:
 #def list_dict_to_string(list_dict):
 #set $file_list = list_dict[0]['additional_input'].__getattr__('file_name')
 #for d in list_dict[1:]:
@@ -18,8 +19,8 @@
 #end for
 #return $file_list
 #end def
-
 --m-barcodes-file=$list_dict_to_string($input_files_mbarcodesfile)
+#end if
 
 
 #if $pnogolayerrorcorrection:
@@ -41,8 +42,8 @@
 cp oerrorcorrectiondetails.qza $oerrorcorrectiondetails
 	]]></command>
 	<inputs>
-		<repeat name="input_files_mbarcodesfile" optional="False" title="--m-barcodes-file">
-			<param label="--m-barcodes-file: Metadata file or artifact viewable as metadata. This option may be supplied multiple times to merge metadata. [required]" name="additional_input" type="data" format="tabular,qza,no_unzip.zip"/>
+		<repeat name="input_files_mbarcodesfile" optional="True" title="--m-barcodes-file [optional]">
+			<param label="--m-barcodes-file: Metadata file or artifact viewable as metadata. This option may be supplied multiple times to merge metadata. [optional]" name="additional_input" type="data" format="tabular,qza,no_unzip.zip"/>
 		</repeat>
 
 		<param format="qza,no_unzip.zip" label="--i-seqs: ARTIFACT RawSequences | EMPSingleEndSequences | EMPPairedEndSequences The single-end sequences to be demultiplexed. [required]" name="iseqs" optional="False" type="data"/>