/*
     * requireNonNull is not safe: Joiner.on(...).join(somethingThatContainsNull) will indeed throw.
     * However, Joiner.on(...).useForNull(...).join(somethingThatContainsNull) *is* safe -- because
     * it returns a subclass of Joiner that overrides this method to tolerate null inputs.
     *
     * Unfortunately, we don't distinguish between these two cases in our public API: Joiner.on(...)

    /*
     * requireNonNull is not safe: Joiner.on(...).join(somethingThatContainsNull) will indeed throw.
     * However, Joiner.on(...).useForNull(...).join(somethingThatContainsNull) *is* safe -- because
     * it returns a subclass of Joiner that overrides this method to tolerate null inputs.
     *
     * Unfortunately, we don't distinguish between these two cases in our public API: Joiner.on(...)