Aggregation is empty if first row value is empty

I use SUM aggregation of the field X. If the node in first row doesn't have a value - SUM is always empty.

Steps to reproduce:

1. Create content type Y with an integer field X
2. Create node of type Y with an empty X field
3. Create node of type Y with a set value for X field
4. Create aggregation view for Y nodes, with SUM of the field X
5. See the empty SUM if the node in the first row doesn't have a value.