New column - If value = null, use value on previous row.

Hi TommyMossberg 

Just use the Fill down feature. Place the following M code in a blank query to see the steps.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjEwMFTSUQpLzClNVYrVAQsYoQgooEsb45HGxwNqNSFTK05eLAA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Got this" = _t, #"Got this.1" = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Got this", Int64.Type}}),
    #"Added Custom" = Table.AddColumn(#"Changed Type", "Custom", each [Got this]),
    #"Filled Down1" = Table.FillDown(#"Added Custom",{"Custom"}),
    #"Reordered Columns" = Table.ReorderColumns(#"Filled Down1",{"Got this", "Custom", "Got this.1"})
in
    #"Reordered Columns"

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Cheers