Member::get() won't return anything

I'm writing a hook that makes use of a logged in user's UID. I tried using Member::getUID(), but the script just stops at that line. I tried Member::get('_uid'), same result.

I edited the method to:

public function get($key, $default=null)
{
    // manage special exceptions
    if ($key == 'name' || $key == 'username') {
        // name is a separate field
        return $this->username;
    } elseif ($key == 'password') {
        // we only ever return the password_hash
        $key = 'password_hash';
    }

    dd(array_get($this->data, $key, $default));
    return array_get($this->data, $key, $default);
}

…and it dumped the expected value. I tried setting array_get()'s output to a var and returning the var, no dice. I tried hardcoding the expected result (return 'my-UID';), but that didn't work either.

I can't get this function to return anything, so I'm stepping away before I punch a hole through my screen.

EDIT:
I'm on Statamic 1.10.4. I also tried 1.10.3, re-installing Statamic, and using an entirely separate installation.