in urn_to_hrn() and hrn_to_urn() if argument is None, just return it

diff --git a/sfa/util/namespace.py b/sfa/util/namespace.py
index 61b05b9..2e4b897 100644 (file)
--- a/sfa/util/namespace.py
+++ b/sfa/util/namespace.py
@@ -57,8 +57,9 @@ def urn_to_hrn(urn):
     """
 
     # if this is already a hrn dont do anything
-    if not urn.startswith(URN_PREFIX):
+    if not urn or not urn.startswith(URN_PREFIX):
         return urn, None
+
     name = urn[len(URN_PREFIX):]
     hrn_parts = name.split("+")
     
@@ -79,7 +80,7 @@ def hrn_to_urn(hrn, type=None):
     convert an hrn and type to a urn string
     """
     # if  this is already a urn dont do anything 
-    if hrn.startswith(URN_PREFIX):
+    if not hrn or hrn.startswith(URN_PREFIX):
         return hrn
 
     authority = get_authority(hrn)