diff --git a/cmd/util.go b/cmd/util.go
index 686fb52..a89a1f0 100644
--- a/cmd/util.go
+++ b/cmd/util.go
@@ -243,6 +243,10 @@ func multiWordReplace(s string, subname string, sub string) string {
 func makeSubstitutions(s string, ext string, m map[string]string) string {
 	for k, v := range m {
 		subst := "$" + k + ext
+		if v == "" {
+			glog.V(2).Info(fmt.Sprintf("No subsitution for '%s'\n", subst))
+			continue
+		}
 		glog.V(1).Info(fmt.Sprintf("Substituting %s with '%s'\n", subst, v))
 		s = multiWordReplace(s, subst, v)
 	}