Question: How to read LuaValue

[xx1adfasd]

I didn't see from the example. When we call scripting_runtime.call_fn, we got a Result<LuaValue, ScriptingError>, and the example only unwraps it.
What if I want to return a bool value from the lua function, and I want to check it's true or false? How to do it?
I can't find information for reading the LuaValue type. It seems to wrap the RegistryKey from lua, but then we neet to get the engine inside LuaRuntime

pub struct LuaRuntime {
    engine: LuaEngine,
}

but it's private. And there's no method to do it as far as I see.