When system receives an unknown field, it breaks

[mpasternak]

Fix this so in case we receive an unknown field name, it won't break

    response = handle_uncaught_exception(request, get_resolver(get_urlconf()), sys.exc_info())
  File "/Users/mpasternak/envs/bpp/lib/python3.6/site-packages/django/core/handlers/exception.py", line 139, in handle_uncaught_exception
    return debug.technical_500_response(request, *exc_info)
  File "/Users/mpasternak/envs/bpp/lib/python3.6/site-packages/django_extensions/management/technical_response.py", line 6, in null_technical_500_response
    six.reraise(exc_type, exc_value, tb)
  File "/Users/mpasternak/envs/bpp/lib/python3.6/site-packages/six.py", line 693, in reraise
    raise value
  File "/Users/mpasternak/envs/bpp/lib/python3.6/site-packages/django/core/handlers/exception.py", line 41, in inner
    response = get_response(request)
  File "/Users/mpasternak/envs/bpp/lib/python3.6/site-packages/django/core/handlers/base.py", line 249, in _legacy_get_response
    response = self._get_response(request)
  File "/Users/mpasternak/envs/bpp/lib/python3.6/site-packages/django/core/handlers/base.py", line 187, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/Users/mpasternak/envs/bpp/lib/python3.6/site-packages/django/core/handlers/base.py", line 185, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/Users/mpasternak/envs/bpp/lib/python3.6/site-packages/django/views/decorators/csrf.py", line 58, in wrapped_view
    return view_func(*args, **kwargs)
  File "/Users/mpasternak/envs/bpp/lib/python3.6/site-packages/django/views/generic/base.py", line 68, in view
    return self.dispatch(request, *args, **kwargs)
  File "/Users/mpasternak/envs/bpp/lib/python3.6/site-packages/django/views/generic/base.py", line 88, in dispatch
    return handler(request, *args, **kwargs)
  File "/Users/mpasternak/envs/bpp/lib/python3.6/site-packages/django/views/generic/base.py", line 155, in get
    context = self.get_context_data(**kwargs)
  File "/Users/mpasternak/envs/bpp/lib/python3.6/site-packages/multiseek/views.py", line 93, in get_context_data
    js_init = registry.recreate_form(form_data)
  File "/Users/mpasternak/envs/bpp/lib/python3.6/site-packages/multiseek/logic.py", line 790, in recreate_form
    result = self.recreate_form_recursive(data['form_data'], info)
  File "/Users/mpasternak/envs/bpp/lib/python3.6/site-packages/multiseek/logic.py", line 765, in recreate_form_recursive
    value = self.get_field_by_name(elem['field']).value_to_web(
AttributeError: 'NoneType' object has no attribute 'value_to_web'