SEPA Export needs better error handling (missing SEPA mandate)

[oe1rfc]

[2020-03-26 12:40:32,476] ERROR in app: Exception on /admin/sepa-export/action/ [POST]
Traceback (most recent call last):
File "/var/lib/housing-admin/venv/lib/python3.7/site-packages/flask/app.py", line 2446, in wsgi_app
response = self.full_dispatch_request()
File "/var/lib/housing-admin/venv/lib/python3.7/site-packages/flask/app.py", line 1951, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/var/lib/housing-admin/venv/lib/python3.7/site-packages/flask/app.py", line 1820, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/var/lib/housing-admin/venv/lib/python3.7/site-packages/flask/_compat.py", line 39, in reraise
raise value
File "/var/lib/housing-admin/venv/lib/python3.7/site-packages/flask/app.py", line 1949, in full_dispatch_request
rv = self.dispatch_request()
File "/var/lib/housing-admin/venv/lib/python3.7/site-packages/flask/app.py", line 1935, in dispatch_request
return self.view_functionsrule.endpoint
File "/var/lib/housing-admin/venv/lib/python3.7/site-packages/flask_admin/base.py", line 69, in inner
return self._run_view(f, *args, **kwargs)
File "/var/lib/housing-admin/venv/lib/python3.7/site-packages/flask_admin/base.py", line 368, in _run_view
return fn(self, *args, **kwargs)
File "/var/lib/housing-admin/venv/lib/python3.7/site-packages/flask_admin/model/base.py", line 2241, in action_view
return self.handle_action()
File "/var/lib/housing-admin/venv/lib/python3.7/site-packages/flask_admin/actions.py", line 117, in handle_action
response = handler0
File "/var/lib/housing-admin/venv/lib/python3.7/site-packages/ff_housing/view/sepa_export.py", line 49, in action_export
sepa.add_invoices(invoices.all())
File "/var/lib/housing-admin/venv/lib/python3.7/site-packages/ff_housing/controller/sepa_export.py", line 78, in add_invoices
self.add_invoice(invoice)
File "/var/lib/housing-admin/venv/lib/python3.7/site-packages/ff_housing/controller/sepa_export.py", line 47, in add_invoice
raise Exception( "%s: No sepa mandate for %s" % (invoice.number, invoice.contact))