Remove unneeded line.
@@ -292,7 +292,6 @@ class Model(object):
self._dirty.add(key) # Mark for dropping on store.
elif key in self._fields: # Fixed
setattr(self, key, self._type(key).null)
- self._dirty.add(key) # Mark for dropping on store.
elif key in self._getters(): # Computed.
raise KeyError(u'computed field {0} cannot be deleted'.format(key))
else:
