[monitoring-plugins] Apparently Dash is not Bash, so -v does not work

[RincewindsHat]

 Module: monitoring-plugins
 Branch: master
 Commit: c1bf69c3a6a52c714e27107219e402bbecd7c000
 Author: RincewindsHat <12514511+RincewindsHat at users.noreply.github.com>
   Date: Mon Dec 20 00:08:24 2021 +0100
    URL: https://www.monitoring-plugins.org/repositories/monitoring-plugins/commit/?id=c1bf69c

Apparently Dash is not Bash, so -v does not work

---

 plugins-scripts/check_log.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/plugins-scripts/check_log.sh b/plugins-scripts/check_log.sh
index d71f420..fdb5741 100755
--- a/plugins-scripts/check_log.sh
+++ b/plugins-scripts/check_log.sh
@@ -212,7 +212,7 @@ elif [ ! -r "$logfile" ] ; then
     exit "$STATE_UNKNOWN"
 fi
 # If no oldlog was given this can not work properly, abort then
-if [ ! -v oldlog ]; then
+if [ -z "$oldlog" ]; then
        echo "Oldlog parameter is needed"
        exit $STATE_UNKNOWN
 fi