Cryptic error messages when filters param is not a key-value store

[bunnrf]

With an empty filters param, Sift encounters:

"undefined method `[]' for nil:NilClass (NoMethodError
filter_params[filter.validation_field] && filter.custom_validate"

And trace points to:
lib/sift/filter_validator.rb:33 in `has_custom_validation?'

Similar errors when filters is something else.

Example query strings:
?filters
?filters=5

I expected an error message similar to the validation error messages Sift returns normally.