use correct params class in declared

lib/grape/dsl/inside_route.rb

@@ -27,6 +27,10 @@ def self.post_filter_methods(type)
       # has completed
       module PostBeforeFilter
         def declared(passed_params, options = {}, declared_params = nil)
+          puts 'declared'
+          puts passed_params
+          puts passed_params.class
+
           options = options.reverse_merge(include_missing: true, include_parent_namespaces: true)
           declared_params ||= optioned_declared_params(options)
 
@@ -46,7 +50,7 @@ def declared_array(passed_params, options, declared_params)
         end
 
         def declared_hash(passed_params, options, declared_params)
-          declared_params.each_with_object({}) do |declared_param, memo|
+          declared_params.each_with_object(passed_params.class.new) do |declared_param, memo|
             # If it is not a Hash then it does not have children.
             # Find its value or set it to nil.
             if !declared_param.is_a?(Hash)
@@ -56,7 +60,7 @@ def declared_hash(passed_params, options, declared_params)
               declared_param.each_pair do |declared_parent_param, declared_children_params|
                 next unless options[:include_missing] || passed_params.key?(declared_parent_param)
 
-                passed_children_params = passed_params[declared_parent_param] || {}
+                passed_children_params = passed_params[declared_parent_param] || passed_params.class.new
                 memo[optioned_param_key(declared_parent_param, options)] = declared(passed_children_params, options, declared_children_params)
               end
             end