Traceback (most recent call last):
  File "electrum/gui/qt/invoice_list.py", line 188, in <lambda>
  File "electrum/gui/qt/send_tab.py", line 585, in do_edit_invoice
  File "electrum/gui/qt/send_tab.py", line 234, in set_payment_identifier
  File "electrum/gui/qt/paytoedit.py", line 214, in try_payment_identifier
AttributeError: 'NoneType' object has no attribute 'strip'