Crash when clicking on red transaction

ERROR:main:async_exception_handler:Task exception was never retrieved
future: <Task finished coro=<history_context_menu() done, defined at /home/moul/projects/sakia/build/src/sakia/gui/transactions_tab.py:167> exception=AttributeError("'NoneType' object has no attribute 'number'",)>
Traceback (most recent call last):
  File "/home/moul/.pyenv/versions/3.5.0/lib/python3.5/asyncio/tasks.py", line 239, in _step
    result = coro.send(value)
  File "/home/moul/projects/sakia/build/src/sakia/gui/transactions_tab.py", line 184, in history_context_menu
    (identity, transfer))
  File "/home/moul/projects/sakia/build/src/sakia/gui/widgets/context_menu.py", line 124, in from_data
    build_actions[type(d)](menu, d)
  File "/home/moul/projects/sakia/build/src/sakia/gui/widgets/context_menu.py", line 97, in _add_transfers_actions
    copy_doc.triggered.connect(lambda checked, number=transfer.blockid.number:
AttributeError: 'NoneType' object has no attribute 'number'