SEBA-198 Fix ONOS synchronizer failing when dependencies set to None

Change-Id: I7228abca290d2f9032365a2d560cddab9e41a349
diff --git a/xos/synchronizer/steps/sync_onos_app.py b/xos/synchronizer/steps/sync_onos_app.py
index cc30645..82e24e3 100644
--- a/xos/synchronizer/steps/sync_onos_app.py
+++ b/xos/synchronizer/steps/sync_onos_app.py
@@ -41,7 +41,9 @@
         :param deps: comma separated list of application names
         :return: bool
         """
-        for dep in [x.strip() for x in str(deps).split(',') if x is not ""]:
+        if not deps:
+            return True
+        for dep in [x.strip() for x in deps.split(',') if x is not ""]:
             try:
                 app = ONOSApp.objects.get(app_id=dep)
                 if not app.backend_code == 1: