${ttl} must exist and be non null

bin/tests/system/dnssec/tests.sh

@@ -2795,10 +2795,10 @@ dig_with_answeropts expiring.example soa @10.53.0.4 > dig.out.ns4.2.$n
 ttls=$(awk '$1 != ";;" {print $2}' dig.out.ns4.1.$n)
 ttls2=$(awk '$1 != ";;" {print $2}' dig.out.ns4.2.$n)
 for ttl in ${ttls:-0}; do
-    [ "${ttl:-0}" -eq 300 ] || ret=1
+    [ "${ttl}" -eq 300 ] || ret=1
 done
 for ttl in ${ttls2:-0}; do
-    [ "${ttl:-0}" -le 60 ] || ret=1
+    [ "${ttl}" -le 60 ] || ret=1
 done
 n=$((n+1))
 test "$ret" -eq 0 || echo_i "failed"