fq3 as optional Values

workflow.wdl

@@ -3,7 +3,7 @@ import "./tasks/mergefq.wdl" as mergefq
 workflow {{ project_name }} {
 	File fq1
 	File fq2
-	File fq3
+	File? fq3
 	String fq_m
 	String disk_size
 	String cluster_config