dropbox storage not working

[benmwendwa]

I want to use dropbox storage in production environment: (https://github.com/robin850/carrierwave-dropbox)
unless Rails.env.production?
storage :file
else
storage :dropbox
# storage :fog
end

but the image url is not being returned. The details being saved in database looks like this:

But the image is being uploaded well. And also other direct controllers and models are working well.
How can I resolve this?