Replace null values with unique values

Anonymous ,

Try this mcode:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WCs7PTVVIzk9JVTBUitWJVgITCEEjbILGSrGxAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Column1 = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Column1", type text}}),
    #"Replaced Value" = Table.ReplaceValue(#"Changed Type","",null,Replacer.ReplaceValue,{"Column1"}),
    #"Grouped Rows" = Table.Group(#"Replaced Value", {"Column1"}, {{"Rows", each if _[Column1]{0} = null then Table.AddIndexColumn(_, "Index", 1,1) else _, type table}}),
    #"Removed Other Columns" = Table.SelectColumns(#"Grouped Rows",{"Rows"}),
    #"Expanded Rows" = Table.ExpandTableColumn(#"Removed Other Columns", "Rows", {"Column1", "Index"}, {"Column1", "Index"}),
    #"Merged Columns" = Table.CombineColumns(Table.TransformColumnTypes(#"Expanded Rows", {{"Index", type text}}, "pt-BR"),{"Column1", "Index"},Combiner.CombineTextByDelimiter("", QuoteStyle.None),"Merged")
in
    #"Merged Columns"

Also, check the attached file.