std::rt::heap::EMPTY

pub const EMPTY: *mut () = 1 as *mut ()

Unstable

: the precise API and guarantees it provides may be tweaked slightly, especially to possibly take into account the types being stored to make room for a future tracing garbage collector

An arbitrary non-null address to represent zero-size allocations.

This preserves the non-null invariant for types like Box<T>. The address may overlap with non-zero-size memory allocations.