Creating a null function pointer using transmute results in undefined behavior, as null function pointers are not valid in Rust.
Instead, use Option<fn()> to safely represent a nullable function pointer.
Code examples
Noncompliant code example
let null_fn: fn() = unsafe { std::mem::transmute(std::ptr::null::<()>()) }; // Noncompliant
Compliant solution
let null_fn: Option<fn()> = None; // Compliant
