Possible type mismatch in property_types.kt

[hanzo2001]

I cloned your repo and opened it in my IDE. An error popped out on line 106 about a type mismatch

Type mismatch.
Required: ParseResult<T>
Found:    ParseResult<out T>

I don't know if this is important because I've just started to learn Kotlin. I am running IntelliJ IDEA 2019.2.3 (Community Edition) Java 1.8.0_121