add nokogiri into Gemfile and fixing dup bug again...

app/models/design.rb

@@ -36,8 +36,10 @@ class Design
   def files=(attrs)
     files = eval(attrs.last)
     attrs[0].each do |a|
-      if(a[:id]=='' && !a[:file].nil?)
-        files.build(:file => a[:file], :to_save => true)
+      if(a[:id]=='' && !a[:file].nil? )
+        if(a[:file]!='')
+          files.build(:file => a[:file], :to_save => true)
+        end
       else
         files.each do |file|
           if file.id.to_s == a[:id]