Fix setting VM property to None

None value should be encoded as empty string.

qubesadmin/base.py

@@ -211,6 +211,8 @@ class PropertyHolder(object):
         else:
             if isinstance(value, qubesadmin.vm.QubesVM):
                 value = value.name
+            if value is None:
+                value = ''
             try:
                 self.qubesd_call(
                     self._method_dest,

qubesadmin/tests/vm/properties.py

@@ -145,7 +145,7 @@ class TC_00_Properties(qubesadmin.tests.vm.VMTestCase):
 
     def test_024_set_none(self):
         self.app.expected_calls[
-            ('test-vm', 'admin.vm.property.Set', 'prop1', b'None')] = \
+            ('test-vm', 'admin.vm.property.Set', 'prop1', b'')] = \
             b'0\x00'
         self.vm.prop1 = None
         self.assertAllCalled()