Citing non existence of a novel idea Can someone please help me out here?

I have a research proposal to present. I had a novel idea to present. 
First things first, I googled the idea and could not find it anywhere. So far so good. So I wrote down in my research proposal that 'No system had implemented (insert my idea here)...'. 

However, when I peer reviewed this writing to a friend, he strongly suggested me to cite the above sentence 'No system..'

My doubt is how do I cite it? I did not find the idea anywhere. 

Is my choice of using this sentence 'No system..' wrong?
It is perfectly fine to write "to the best of our knowledge" -- assuming you really made a thorough search. It is especially important that you look up all research papers that try to solve similar problems and confirm that they do not use the idea you propose (maybe in disguise). If you find something broadly similar, cite it, and discuss what makes your idea different to the one you found.