Combine two influxdb queries and add values

Hello, below is my query. I want to compbine two queries into one graph. The query inspector shows me a lot of null values. If I add A+A then the result is correct.

0:Object

name:“dataa”

columns:Array[2]

values:Array[11]

1:Object

name:“datab”

columns:Array[2]

0:“time”

1:“last_last”

values:Array[11]

0:Array[1607817600000,null]

1:Array[1607904000000,null]

2:Array[1607990400000,null]

3:Array[1608076800000,null]

4:Array[1608163200000,null]

5:Array[1608249600000,null]

6:Array[1608336000000,null]

7:Array[1608422400000,null]

8:Array[1608508800000,null]

9:Array[1608595200000,null]

10:Array[1608681600000,null]

Query:

SELECT last(“A”)
+ last(“B”)

FROM (
SELECT (non_negative_difference(last(“value”)) )
AS “A”
FROM “dataa”
WHERE $timeFilter
), (
SELECT (non_negative_difference(last(“value”)) )
AS “B”
FROM “datab”
WHERE $timeFilter
)
GROUP BY time(1d)