i have some math function using lens formula, and when i use last_value function when it's doesn't match my filter i want some default value like 0.
but now it's return nothing and all the result for my formula become - .
For example
last_value(tran.target_volume, kql='shop.sale_office: "Office 1" ') +
last_value(tran.target_volume, kql='shop.sale_office: "Office 2"')
for Office2 there are no data for sales , and return null and my result become " - ".