drupal 7 hidden views blocks when node references value is empty I created Expert and Review content types, both have a node reference field related each other.

Expert
    - title
    - field_expert_reviews(node reference)

Review
    - title
    - field_review_expert(node reference)


I follow this tutorial create a block show expert's review in the side bar. But I found that when the field_expert_reviews is empty, the block doesn't hidden. How to hidden the block when the node reference field is empty?
You need to add a Filter Criteria which validates to "Is not empty (NOT NULL)" on the field which should not be empty.