I have a collection with 2 documents such as:

• {_id: 1, test: 1}
• {_id: 2, test: null}

On this collection, I have 1 index such as:

• {test: 1}

Explain a query tell me that :

• query on {test: 1}

  is a covered query.

• query on {test: null}

  is not.

How could I use a covered query in this specific case to use my index without needing to scan the collection ?

Thanks.