correct workflow problem

models/workflow/workflow.go

@@ -21,6 +21,9 @@ type AbstractWorkflow struct {
 }
 
 func (w *AbstractWorkflow) isDCLink(link graph.GraphLink) (bool, string) {
+	if w.Graph == nil || w.Graph.Items == nil {
+		return false, ""
+	}
 	if d, ok := w.Graph.Items[link.Source.ID]; ok && d.Datacenter != nil {
 		return true, d.Datacenter.UUID
 	}