future proofing is good, but...

since print() was made a function in py3, i can predict at some point
that return will be made a func as well. sure, good.
but "return()" *currently* returns an empty tuple. We want to
explicitly return None for testing purposes.

aif/system/services.py

@@ -57,4 +57,4 @@ class ServiceDB(object):
             else:
                 if os.path.exists(dest_path):
                     os.remove(dest_path)
-        return()
+        return(None)