cannot search for modern surname without a forename

[SaraUckelman]

You broke it!
This is why we can't have nice things!

The exception was:

Traceback (most recent call last):
File "/home/op/dw_op/viewer.py", line 399, in search
return search_modern(get_db().cursor(), surname, forename)
File "/home/op/dw_op/viewer.py", line 329, in search_modern
return render_template('choose_person.html', matches=matches)
File "/usr/lib/python3.6/site-packages/flask/templating.py", line 134, in render_template
context, ctx.app)
File "/usr/lib/python3.6/site-packages/flask/templating.py", line 116, in _render
rv = template.render(context)
File "/usr/lib/python3.6/site-packages/jinja2/asyncsupport.py", line 76, in render
return original_render(self, *args, **kwargs)
File "/usr/lib/python3.6/site-packages/jinja2/environment.py", line 1008, in render
return self.environment.handle_exception(exc_info, True)
File "/usr/lib/python3.6/site-packages/jinja2/environment.py", line 780, in handle_exception
reraise(exc_type, exc_value, tb)
File "/usr/lib/python3.6/site-packages/jinja2/_compat.py", line 37, in reraise
raise value.with_traceback(tb)
File "/home/op/dw_op/templates/choose_person.html", line 1, in top-level template code
{% extends "base.html" %}
File "/home/op/dw_op/templates/base.html", line 37, in top-level template code
{% block content %}{% endblock %}
File "/home/op/dw_op/templates/choose_person.html", line 10, in block "content"
{{i[2]}} {{i[1]}}
File "/usr/lib/python3.6/site-packages/flask/helpers.py", line 333, in url_for
return appctx.app.handle_url_build_error(error, endpoint, values)
File "/usr/lib/python3.6/site-packages/flask/app.py", line 1805, in handle_url_build_error
reraise(exc_type, exc_value, tb)
File "/usr/lib/python3.6/site-packages/flask/_compat.py", line 33, in reraise
raise value
File "/usr/lib/python3.6/site-packages/flask/helpers.py", line 323, in url_for
force_external=external)
File "/usr/lib/python3.6/site-packages/werkzeug/routing.py", line 1768, in build
raise BuildError(endpoint, values, method, self)
werkzeug.routing.BuildError: Could not build url for endpoint 'person' with values ['surname']. Did you forget to specify values ['forename']?

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/usr/lib/python3.6/site-packages/flask/app.py", line 1612, in full_dispatch_request
rv = self.dispatch_request()
File "/usr/lib/python3.6/site-packages/flask/app.py", line 1598, in dispatch_request
return self.view_functionsrule.endpoint
File "/home/op/dw_op/viewer.py", line 413, in search
flash(e.message, 'error')
AttributeError: 'BuildError' object has no attribute 'message'