undefined method `strip' for #<ActionController::UploadedStr

i am getting array of uploaded images when i am trying to dump in
database i am getting error

<strong>NoMethodError (undefined method `strip' for
#<ActionController::UploadedStringIO:0x458afe4>):
    /vendor/plugins/attachment_fu/lib/technoweenie/attachment_fu.rb:367:in
`sanitize_filename'
    /vendor/plugins/attachment_fu/lib/technoweenie/attachment_fu/backends/file_system_backend.rb:48:in
`filename='
</strong>

help ?