Previously, this would assume a given type, and likely raise
NoMethodError if the type was not what was expected. If there
is a typecast error when rendering the validation failure
template, display a simple error page. This should only happen
if a user monkeys around with a form parameter before submitting
the request.
This uses a new feature in the Roda typecast_params plugin, so
update to the latest Roda commit.
23601a07a3