Create Columns with given name if it doesn't exist.

Hi Anonymous 

What are the values in those newly created columns? Here is one sample to have the same value with the column name

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WKkktLlHSwUbFxgIA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [level1 = _t, level2 = _t, level3 = _t, level4 = _t]),
    columnList = {"level1","level2","level3","level4","level5","level6","level7","level8","level9","level10"},
    fxAddColumn = (T as table, N as number) =>
         [
             newColumns=List.Difference(columnList, Table.ColumnNames(Source)),
             counter = List.Count(newColumns),
             columnName = newColumns{N},
             tempTable = Table.AddColumn(T, columnName, each columnName),
             result = if N>= counter-1 then tempTable else @fxAddColumn(tempTable,N+1) 
         ][result], 

    Custom = fxAddColumn(Source,0)

in
    Custom