Better test for variable undefined

gitlab/functions.sh

@@ -27,7 +27,7 @@ log_error() {
 
 # Checks a given environment variable is set (non-zero size)
 check_env() {
-  if [ -z "${!1}" ]; then
+  if [ -z "${1+abc}" ]; then
     log_error "Variable ${1} is undefined - aborting...";
     exit 1
   else
@@ -38,7 +38,7 @@ check_env() {
 
 # Exports a given environment variable, verbosely
 export_env() {
-  if [ -z "${!1}" ]; then
+  if [ -z "${1+abc}" ]; then
     log_error "Variable ${1} is undefined - aborting...";
     exit 1
   else
@@ -50,7 +50,7 @@ export_env() {
 
 # Checks a given environment variable is set (non-zero size)
 check_pass() {
-  if [ -z "${!1}" ]; then
+  if [ -z "${1+abc}" ]; then
     log_error "Variable ${1} is undefined - aborting...";
     exit 1
   else