PQ - Sum columns with null values

Left	Right	_____	Left	Right	Sum
2			2		2
	7			7	7
3	8		3	8	11
4	9		4	9	13
	10			10	10
|
5			5		5
6	11		6	11	17

Code:

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let
    Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
    ListSum = Table.AddColumn(Source, "Sum", each List.Sum({[Left],[Right]}))
in
    ListSum

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