zig c pointer question

cast.zig

const c = @cImport({
    @cInclude("cfile.h");
});

pub fn main() void {
    var x:?[*]const u8 = null;
    x = c.some_func(0);
}

cfile.h

const char* some_func(int a)
{
  if(a == 0)
    return 0;
  return "FOO";
}

Works:

pub fn main() void {
    var x: ?[*]const u8 = @intToPtr([*c]u8, 0);
    x = null;
}

Also works:

pub fn main() void {
    var x: ?[*]const u8 = null;
    x = @intToPtr(?[*]u8, 0);
}

Doesn't work:

pub fn main() void {
    var x: ?[*]const u8 = null;
    x = @intToPtr([*c]u8, 0);
}