Converts a value to a double. If the value cannot be converted to an double, $toDouble errors. If the value is null or missing, $toDouble returns null.
4.0
https://www.mongodb.com/docs/manual/reference/operator/aggregation/toDouble/#mongodb-expression-exp.-toDouble
Converts a value to a double. If the value cannot be converted to an double, $toDouble errors. If the value is null or missing, $toDouble returns null.