Allow the creation of empty collections

Fix #201

radicale/xmlutils.py

@@ -128,8 +128,11 @@ def name_from_path(path, collection):
 def props_from_request(root, actions=("set", "remove")):
     """Return a list of properties as a dictionary."""
     result = OrderedDict()
+    if root:
         if not hasattr(root, "tag"):
             root = ET.fromstring(root.encode("utf8"))
+    else:
+        return result
 
     for action in actions:
         action_element = root.find(_tag("D", action))