How to search for strings in mupdf?

I am using mupdf in my ubuntu 14.04 system. I like this pdf reader because its fast, light weight and doesn't clog my memory and CPU. But it becomes some times hard to use because of the lack of some function for example a search bar. After searching I found that in mupdf we can search strings using n/N function.

But when I type string "prime" and then press n it shows only this (also because of the presence of i in prime my background color is inverted)

Warning: String '' not found

so how should I search strings in mupdf?

You can use this :

/      Search for text. 
n, N   Find the next/previous search result.

More useful information here:
Is there a comprehensive list of mupdf keyboard shortcuts?