diff --git a/lib/jsonapi/scopes/filters.rb b/lib/jsonapi/scopes/filters.rb
index 028eea4..15e8edb 100644
--- a/lib/jsonapi/scopes/filters.rb
+++ b/lib/jsonapi/scopes/filters.rb
@@ -19,7 +19,7 @@ def apply_filter(params)
         filtering_params = params.dig(:filter) || {}
 
         filtering_params.each do |key, value|
-          value = value.to_s.split(',').reject(&:blank?) if value.include?(',')
+          value = value.to_s.split(',').reject(&:blank?) if value&.include?(',')
 
           raise InvalidAttributeError, "#{key} is not valid as filter attribute." unless @filters.include?(key.to_sym)
 
diff --git a/lib/jsonapi/scopes/includes.rb b/lib/jsonapi/scopes/includes.rb
index 9f29a18..2aea1d7 100644
--- a/lib/jsonapi/scopes/includes.rb
+++ b/lib/jsonapi/scopes/includes.rb
@@ -21,11 +21,15 @@ def apply_include(params = {}, options = { allowed: [] })
 
         allowed_fields = (Array.wrap(options[:allowed]).presence || @allowed_includes).map(&:to_s)
 
-        fields.split(',').each do |field|
+        a_fields = fields.split(',')
+        a_fields.each do |field|
           raise InvalidAttributeError, "#{field} is not valid as include attribute." unless allowed_fields.include?(field)
         end
 
-        records.includes(convert_includes_as_hash(fields))
+        preload_fields = a_fields.select { |field| reflect_on_association(field).polymorphic? }
+        include_fields = a_fields - preload_fields
+        records.includes(convert_includes_as_hash(include_fields.join(',')))
+        records.preload(convert_includes_as_hash(preload_fields.join(',')))
       end
 
       private
diff --git a/lib/jsonapi/scopes/sorts.rb b/lib/jsonapi/scopes/sorts.rb
index ee7a6ce..badfa3c 100644
--- a/lib/jsonapi/scopes/sorts.rb
+++ b/lib/jsonapi/scopes/sorts.rb
@@ -29,9 +29,20 @@ def apply_sort(params = {}, options = { allowed: [], default: {} })
           raise InvalidAttributeError, "#{field} is not valid as sort attribute." unless allowed_fields.include?(field)
         end
 
-        order = ordered_fields.presence || default_order
+        res = self
 
-        self.order(order)
+        order_to_follow = ordered_fields.presence || default_order
+        order_to_follow.each do |single_order_q, direction|
+          if single_order_q.to_s.include? 'scope:'
+            scope_name = single_order_q.to_s.split(':').last
+
+            res = send(scope_name.to_sym, direction)
+          else
+            res = order("#{single_order_q}": direction)
+          end
+        end
+
+        res
       end
 
       private