Check if vars are empty

github/check.adguard.update

@@ -85,6 +85,33 @@ error_message() {                                               # {{{
 	exit "${local_error_code:=66}"
 }
 # }}}
+is_var_empty() {                                                # {{{
+
+	## Return False by default
+	return_var_empty="1"
+	## Total number of variables to test
+	local_total_var="${#}"
+
+	loop_count_var_empty="0"
+
+	## While it remains a variable to test
+	while [ "${local_total_var}" -gt "${loop_count_var_empty}" ]; do
+		debug_message "is_var_empty − \
+Test var: ${1}."
+		### Test if this is empty and set return value to True
+		[ -z "${1}" ] && return_var_empty="0"
+
+		### Increase the number of tested variables
+		loop_count_var_empty=$((loop_count_var_empty+1))
+
+		### Shift to the next variable
+		shift
+	done
+
+	return "${return_var_empty}"
+
+}
+# }}}
 define_vars() {                                                 # {{{
 
 	## If adguard_bin wasn't defined (argument,...) {{{
@@ -116,6 +143,17 @@ main() {                                                        # {{{
 	## Define all vars according to selected options
 	define_vars
 
+	## Test adguard_current_version
+	##   AND exit with error 2
+	is_var_empty "${adguard_current_version}" \
+		&& error_message "adguard_current_version seems empty (${adguard_current_version})." 2
+
+	## Test adguard_new_version
+	##   AND exit without error
+	is_var_empty "${adguard_new_version}" \
+		&& debug_message "adguard_new_version seems empty (${adguard_new_version}), exit without error." \
+		&& exit 0
+
 	## Check if the current version is the last one {{{
 	if [ "${adguard_current_version}" != "${adguard_new_version}" ]; then
 		debug_message "Test AdGuard Home version − \