what suitable volume error-checking?

public vacant publicmethod(foobar foobar)
{
    (foobar == null)
        pitch new argumentnullexception("foobar", "foobar can't null");

    // record [added:  interjection s.lott]
    _logger.log("publicmethod called foobar category " + foobar.classification);

    int movement = determineaction();
    privatemethod(foobar, action);
}

private vacant privatemethod(foobar foobar, int action)
{
    (foobar == null)
        pitch new argumentnullexception("foobar", "foobar can't null");  // line superfluous?

    /*
        something
    */
}

is ok skip kind blunder checking private methods quarrel already checked open interface? wholly there's arrange rule-of-thumb by...

edit:

maybe argumentnullexception isn't such good instance since justification finished should check during both levels nonetheless relapse opposite blunder messages.