Improve constraints parsing for empty values

diff --git a/juju/constraints.py b/juju/constraints.py
index c551883..998862d 100644 (file)
--- a/juju/constraints.py
+++ b/juju/constraints.py
@@ -39,10 +39,7 @@ def parse(constraints):
     and key value pairs joined by an '='.
 
     """
-    if constraints is None:
-        return None
-
-    if constraints == "":
+    if not constraints:
         return None
 
     if type(constraints) is dict: