Filter values for related resources are wrapped in nested arrays?

I'm a little confused as to what's going on, but upgrading from 0.8.3 to 0.9 broke some filters I have in place. e.g.:

VERIFY_RADIUS_FILTER = ->(value, context) {
  return NoLimit.new unless context[:current_location].present?

  value
}

FILTER_RADIUS_FROM_LOCATION = ->(records, value, options) {
  location = options.dig(:context, :current_location)
  limit = Array(value).first

  return records unless location.present? && limit.present?

  records.near(location, Float(limit))
}

filter :radius, default: 100.0,
                verify: VERIFY_RADIUS_FILTER,
                apply: FILTER_RADIUS_FROM_LOCATION

I think this commit my be the culprit? https://github.com/cerebris/jsonapi-resources/commit/3a691b29adb3e7aff0743ef59e44556bedb260c9

From what I can tell, this results in Resource#verify_resource being called twice. For a custom filter, at least (which is what I've got), that means the raw value gets doubly-nested in an array: https://github.com/cerebris/jsonapi-resources/blob/19f4d7b59f92b05fa28c4f925391cf5998123308/lib/jsonapi/resource.rb#L753

Instead I wonder if that line should be something like:

filter_values += raw.is_a?(String) ? CSV.parse_line(raw) : Array(raw)

To make sure we don't wrap an array?

/cc @hidde-jan

Start at lib/jsonapi/resource.rb around line 753 and compare the filter-value handling with commit 3a691b2. Reproduce the custom-filter case described in the issue, checking whether Resource#verify_resource causes nested arrays. Done means related-resource filter values are not unnecessarily wrapped while string parsing still works; no test file is named in the issue.