## Why does Sorbet think this is `nil`? I just checked that it's not!| sorbet.org
Recall from [Enabling runtime checks](/docs/runtime) that `sorbet-runtime` raises| sorbet.org
Sorbet is a gradual type checker, which is a blessing and a curse.| sorbet.org
There are five ways to assert the types of expressions in Sorbet:| sorbet.org
This is one of three docs aimed at helping answer common questions about Sorbet:| sorbet.org
| sorbet.org
As we've mentioned before, Sorbet is a [gradual](/docs/gradual) system: it can be| sorbet.org
RBI files are "Ruby Interface" files. Sorbet uses RBI files to learn about| sorbet.org