diff --git a/script/yaml.sh b/script/yaml.sh
index cda48d4..ec5ece5 100755
--- a/script/yaml.sh
+++ b/script/yaml.sh
@@ -5,7 +5,7 @@
 
 parse_yaml() {
     local yaml_file=$1
-    local prefix=$2
+    local prefix=${2:-}
     local s
     local w
     local fs
@@ -71,6 +71,6 @@ create_variables() {
 
 # Execute parse_yaml() direct from command line
 
-if [ "x" != "x${1}" ] && [ "x--debug" != "x${1}" ]; then
-    parse_yaml "${1}" "${2}"
+if [ "x" != "x${1:-}" ] && [ "x--debug" != "x${1:-}" ]; then
+    parse_yaml "${1}" "${2:-}"
 fi