修复

app/controllers/api/v1/issues/milestones_controller.rb

@@ -70,11 +70,16 @@ class Api::V1::Issues::MilestonesController < Api::V1::BaseController
   end
 
   def sort_by 
-    Version.columns.include?(params.fetch(:sort_by, "created_on")) ? params.fetch(:sort_by, "created_on") : "created_on"
+    sort_by = params.fetch(:sort_by, "created_on")
+    sort_by = Version.column_names.include?(sort_by) ? sort_by : "created_on"
+
+    sort_by
   end
 
-  def sort_direction 
-    %w(desc asc).include?(params.fetch(:sort_direction, "desc")) ? params.fetch(:sort_direction, "desc") : "desc"
+  def sort_direction
+    sort_direction = params.fetch(:sort_direction, "desc").downcase
+    sort_direction = %w(desc asc).include?(sort_direction) ? sort_direction : "desc"
+    sort_direction
   end
 
 end