error: transmuting a known null pointer into a function pointer
  --> $DIR/transmute_null_to_fn.rs:8:23
   |
LL |         let _: fn() = std::mem::transmute(0 as *const ());
   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this transmute results in undefined behavior
   |
   = help: try wrapping your function pointer type in `Option<T>` instead, and using `None` as a null pointer value
   = note: `-D clippy::transmute-null-to-fn` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(clippy::transmute_null_to_fn)]`

error: transmuting a known null pointer into a function pointer
  --> $DIR/transmute_null_to_fn.rs:10:23
   |
LL |         let _: fn() = std::mem::transmute(std::ptr::null::<()>());
   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this transmute results in undefined behavior
   |
   = help: try wrapping your function pointer type in `Option<T>` instead, and using `None` as a null pointer value

error: transmuting a known null pointer into a function pointer
  --> $DIR/transmute_null_to_fn.rs:21:23
   |
LL |         let _: fn() = std::mem::transmute(ZPTR);
   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^ this transmute results in undefined behavior
   |
   = help: try wrapping your function pointer type in `Option<T>` instead, and using `None` as a null pointer value

error: aborting due to 3 previous errors