Custom column failing to add to together numerical columns

[masplin]

I have 4 numerical columns that i tried to add together by just putting a "+" between the field names using the wizard, but it just produces null values.  the query is below

= Table.AddColumn(#"Changed Type7", "Custom", each [#"Exceptional Items pre GP#(lf)th GBP Last avail. yr"]+[#"Exceptional Items pre OP#(lf)th GBP Last avail. yr"]+[#"Exceptional Items#(lf)th GBP Last avail. yr"]+[#"Other Exceptional Items#(lf)th GBP Last avail. yr"])

However i found if I select the columns and use the statisitcs/sum function it works and query looks like this

= Table.AddColumn(#"Added Custom9", "Exceptionals", each List.Sum({ [#"Exceptional Items pre GP#(lf)th GBP Last avail. yr"],[#"Exceptional Items pre OP#(lf)th GBP Last avail. yr"],[#"Exceptional Items#(lf)th GBP Last avail. yr"],[#"Other Exceptional Items#(lf)th GBP Last avail. yr"]}),type number)

Can someone explain why just putting a "+" between field names doesn't work as sure i've used convetional mathematical operators before in custom columns?

Thanks for any advice

Mike

[Zubair_Muhammad · Accepted solution]

@masplin

You might have null values in some columns

null + 10 = null in Power Query/M
But
List.Sum({10,null})=10

[masplin]

Yes lots of them. Thought a null was a blank, but there you go thanks for clarifyingi'm not doing somethig wrong