given arg_one require arg_two of array -> auto passes empty string to array when empty array is given

[dejoma]

desc 'Breaking Grape', security: [jwt: []], success: { code: 201, model: SomeRepresenter }
      params do
        with documentation: { param_type: 'body' } do
          requires :arg_one, type: String, values: %w[one two three]
          given arg_one: ->(type) { type == 'two' } do
            requires :arg_two, type: Array[String], allow_blank: false
          end
        end
      end
end

POST to that endpoint with { "arg_one": "two", "arg_two": [] }
and somehow the array will contain an empty string. Fails both with allow_blank false and allow_blank.

How does the empty string end up there?
How does it not fail when allow_blank false?

[dblock]

1. Does it work if type is not an array (e.g. String)?
2. Does it work without given?
3. Confirm the version of Grape and Rack, could be related to Rack3 breaking change with query param nil #2298.

Probably a bug in some combination. Would appreciate a unit test that reproduces the problem in a pull request.