How can I check that UVariable is nullable type?

[Kolyall]

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