Maybe unsound in RLocal::new

Hello, thank you for your contribution in this project, I am scanning the unsoundness problem in rust project.
I notice the following code:

pub struct RLocal<T: Copy> {
    old_value: T,
    variable: *mut T,
}

impl<T> RLocal<T>
where
    T: Copy,
{
    pub fn new(new_value: T, variable: *mut T) -> RLocal<T> {
        unsafe {
            let old_value = libr::get(variable);
            libr::set(variable, new_value);

            Self {
                old_value,
                variable,
            }
        }
    }
}

Considering that pub mod raii, and new is also a pub function. I assume that users can directly call this function. This potential situation could result in libr::get being called to a null pointer, and might trigger undefined behavior (UB). For safety reasons, I felt it necessary to report this issue. If you have performed checks elsewhere that ensure this is safe, please don’t take offense at my raising this issue.
I suggest Several possible fixes:

1. If there is no external usage for RLocal or new, they should not marked as pub, at least its new should not marked as pub
2. new method should add additional check for null pointer.
3. mark new method as unsafe and proper doc to let users know that they should provide valid Pointers.

Inizia individuando il modulo pubblico raii e RLocal::new, quindi esamina i chiamanti e le assunzioni sui puntatori relative a libr::get e libr::set. Determina se l'API può ricevere un puntatore nullo o comunque non valido; il lavoro è completato quando il contratto di sicurezza o la visibilità sono inequivocabili e il percorso di comportamento indefinito segnalato è stato risolto.