--- jrtangle.old	2015-01-12 20:35:08.518843185 +0200
+++ jrtangle	2015-01-12 20:35:09.822843239 +0200
@@ -413,6 +413,8 @@
 	if (NF != 4)
 		fatal(_"usage: @file_update name dir suffix\n")
 
+	if ($4 == "\"\"")
+		$4 = ""
 	Update_value[$2]["DIR"] = $3
 	Update_value[$2]["SUFFIX"] = $4