I tried it and got a lot of false positives, but there wasn't so much output that I couldn't quickly pick out the interesting cases. This is very cool.
We'd be interested in the general characteristics of the most common ones you are seeing. If you have a chance to file a couple issues (and haven't done so yet): https://github.com/uber-go/nilaway/issues
We definitely have gotten some useful reports there already since the blog post!
We are aware of a number of sources of false positives and actively trying to drive them down (prioritizing the patterns that are common in our codebase, but very much interested in making the tool useful to others too!).
Some sources of false positives are fundamental (any non-trivial type system will forbid some programs which are otherwise safe in ways that can't be proven statically), others need complex in-development features for the tool to understand (e.g. contracts, such as "foo(...) returns nil iff its third argument is nil"), and some are just a matter of adding a library model or similar small change and we just haven't run into it ourselves.
In one case, it couldn’t tell that a slice couldn’t go out of bounds because I was iterating through it backwards instead of forwards. In another case, I had a helper method on a type to deal with initializing a named map type, but it couldn’t see that and thought the map was going to explode from being nil. Those are two false positives I remember off the top of my head. I can look it up again later.