add error if no response

checks/check_snmp_linux.py

@@ -136,6 +136,8 @@ class SNMPDiskResource(nagiosplugin.Resource):
         disks = dict()
         for key,value in oids.items():
             results[key] = self.session.walk(baseoid + value)
+            if len(results[key]) <= 0:
+                raise ValueError('no values from snmp')
         for key, value in results.items():
             for item in value:
                 if key == 'dskIndex':