Question about Box from null

[Nugine]

For example, I see a function that is exported via extern "Rust" in cxx::brige. (deepseek-ai/3FS#11)

fn create(path: &str, create: bool, prefix_len: usize, error: Pin<&mut CxxString>) -> Box<Engine> {
    let config = EngineConfig {
        path: PathBuf::from(path),
        create,
        prefix_len,
    };
    match Engine::open(&config) {
        Ok(engine) => Box::new(engine),
        Err(e) => {
            error.push_str(&e.to_string());
            unsafe { Box::from_raw(std::ptr::null_mut()) }
        }
    }
}

unsafe { Box::from_raw(std::ptr::null_mut()) }

Is this line a UB even if the Box is exported to C++ side?

And if it is UB, what is the recommanded way to fix? Raw pointer?