How can I check that UVariable is nullable type?

I didnt find an answer for the question in the doc (https://googlesamples.github.io/android-custom-lint-rules/)
I want to check that variable is nullable type. For example:
an fun for `UVariable`:
```
fun isNullable(uVariable: UVariable): Boolean {
}
```
for `var value: Strings` should return false
for `var value: Strings?` should return true