Power Query ; Table Replace Error problem

Hi Dicken,

Thank you for reaching out to the Microsoft Fabric Forum community.

I’ve reproduced the scenario using your sample data and for your reference, I’m attaching the output screenshot and the .pbix file. Thanks, dufoq3 for providing your insights.

let Source = #table(type table [A = text, B = text], {{"a", "b"}, {"a", "c"}, {"d", "f"}, {"c", "d"}}), reclist = List.InsertRange(Table.ToRecords(Source), 2, {"", ""}), Transformed = List.Transform(reclist, each if Value.Is(_, Record.Type) then _ else [A = null, B = null]), ToTbl = Table.FromRecords(Transformed, null, MissingField.UseNull), 

ReplaceNulls = Table.ReplaceValue(ToTbl, null, "", Replacer.ReplaceValue, {"A", "B"}) 
 

in ReplaceNulls 

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Thank you.