Merge pull request #127 from davidnewhall/dn2_fix_crash

protect against nil return values

core/poller/unifipoller/unifi.go

@@ -115,6 +115,9 @@ func (u *UnifiPoller) CollectMetrics() (*Metrics, error) {
 // This is where we can manipuate the returned data or make arbitrary decisions.
 // This function currently adds parent device names to client metrics.
 func (u *UnifiPoller) AugmentMetrics(metrics *Metrics) error {
+	if metrics == nil || metrics.Devices == nil || metrics.Clients == nil {
+		return fmt.Errorf("nil metrics, augment impossible")
+	}
 	devices := make(map[string]string)
 	bssdIDs := make(map[string]string)
 	for _, r := range metrics.UAPs {