android - org.jetbrains? それは何ですか？

Question

I recently cloned the ics-openvpn project: https://code.google.com/p/ics-openvpn/source/checkout

But when I opened the project, it gave me some errors considering these lines not being resolved:

import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

I tried searching it on the internet, but I got no clear answer. So my question is: What is 'jetbrains'? How do I resolve this?

Thanks