plugin invitations: on modify an empty value delete corresponding extra keys, and reserved keys are now ignored.

src/plugins/plugin_misc_invitations.py

@@ -294,6 +294,7 @@ class InvitationsPlugin(object):
 
         @param id_(unicode): UUID linked to an invitation
         @param new_extra(dict[unicode, unicode]): data to update
+            empty values will be deleted if replace is True
         @param replace(bool): if True replace the data
             else update them
         @raise KeyError: there is not invitation with this id_
@@ -310,7 +311,16 @@ class InvitationsPlugin(object):
             else:
                 new_data = current_data
                 for k,v in new_extra.iteritems():
-                    new_data[k] = v
+                    if k in EXTRA_RESERVED:
+                        log.warning(_(u"Skipping reserved key {key}".format(k)))
+                        continue
+                    if v:
+                        new_data[k] = v
+                    else:
+                        try:
+                            del new_data[k]
+                        except KeyError:
+                            pass
 
             self.invitations[id_] = new_data