Null Props Cause Incorrect Query Estimation

Using null props in a query can cause the query engine to incorrectly estimate the cost of query plan which can lead to a traversal and slow queries to execute.

If you look at the query plan below the number of null props documents is quiet high yet the cost for the query is only 19. When we execute the UNION query the cost is 38 which is why it is not selected when in reality the original cost should be much higher.

After removing the null check the cost estimation is drastically different and correctly reflects the number of documents in the index.