Fix Bug on Events Configuration Equal function

If Config.Events was nil, it would cause an null pointer exception

pkg/notification/notification.go

@@ -192,9 +192,18 @@ func (t *Config) Equal(events []EventType, prefix, suffix string) bool {
 		newFilter = append(newFilter, FilterRule{Name: "suffix", Value: suffix})
 	}
 
-	passFilters := EqualFilterRuleList(t.Filter.S3Key.FilterRules, newFilter)
-	// if it matches events and filters, mark the index for deletion
-	return passEvents && passFilters
+	if len(newFilter) > 0 {
+		// compare newFilter with Config.Filter
+		if t.Filter != nil {
+			passFilters := EqualFilterRuleList(t.Filter.S3Key.FilterRules, newFilter)
+			return passEvents && passFilters
+		}
+		// if Config is nil, they are not equal
+		return false
+	}
+
+	// if matches events and t.filter == nil
+	return (t.Filter == nil) && passEvents
 }
 
 // TopicConfig carries one single topic notification configuration