zig/doc/langref/checking_null_in_zig.zig

const Foo = struct{};
fn doSomethingWithFoo(foo: *Foo) void { _ = foo; }

fn doAThing(optional_foo: ?*Foo) void {
    // do some stuff

    if (optional_foo) |foo| {
      doSomethingWithFoo(foo);
    }

    // do some stuff
}

// syntax