if(!is_null(variable) && is_integer(variable))
{
    if(variable == 0)
        do_zero();
    elseif(variable == 1)
        do_one();
    elseif(variable == 2)
        do_two();
    else
        throw_error();
}

if(!is_null(variable) && is_integer(variable))
{
    if(variable == 0)
        do_zero();
    if(variable == 1)
        do_one();
    else
        do_two();
}