return undef if initiating snmp session fails

diff --git a/upsgraph.pl b/upsgraph.pl
index 100c52b1f38c1a2ec2274ede6c4b6000cff672d2..9887d0c4ab2215e9b20eaecd4abf0cc23de55292 100755 (executable)
--- a/upsgraph.pl
+++ b/upsgraph.pl
@@ -58,6 +58,7 @@ sub fetch_snmp(@) {
 
        if (!$session) {
                print STDERR "session error: $error";
+               return undef;
        }
 
        $session->translate(0);