when there is no purchase order, ItemIndex::get() returned false, it would lead RecommendController::do_recommend() return error message.
when there is no purchase order, ItemIndex::get() returned false,
it would lead RecommendController::do_recommend() return error message.

to avoid this error message and return empty recommend result,
make ItemIndex::get() return true when docs result is empty.

izenecloud/sf1r-lite,izenecloud/sf1r-ad-delivery,izenecloud/sf1r-lite,izenecloud/sf1r-lite,pombredanne/sf1r-lite,izenecloud/sf1r-ad-delivery,pombredanne/sf1r-lite,izenecloud/sf1r-ad-delivery,izenecloud/sf1r-ad-delivery,pombredanne/sf1r-lite,izenecloud/sf1r-lite,izenecloud/sf1r-lite,pombredanne/sf1r-lite,pombredanne/sf1r-lite,izenecloud/sf1r-ad-delivery