fix bug that causes a slice with no nodes to have an in incorrect rspec

diff --git a/sfa/plc/plaggregate.py b/sfa/plc/plaggregate.py
index 55e6291..b0c78d1 100644 (file)
--- a/sfa/plc/plaggregate.py
+++ b/sfa/plc/plaggregate.py
@@ -138,7 +138,7 @@ class PlAggregate:
     def get_nodes_and_links(self, slice=None,slivers=[], options={}):
         # if we are dealing with a slice that has no node just return 
         # and empty list    
-        if slice is not None and not slice['node_ids']:
+        if not slice or  not slice['node_ids']:
             return ([],[])
 
         filter = {}