Return values in Power Query based on condition

This isn't a very elegant solution but it's the first thing that I came up with:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMlPSUVKK1YlWsgAyLMAsS5iQKYxhjMEwATJMwCxDDDm4keZAhjmYZQQTgjBiAQ==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Column 1" = _t, #"Column 2" = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Column 1", Int64.Type}, {"Column 2", Int64.Type}}),
    Boolean = List.Transform(#"Changed Type"[Column 2], each if _ <> null then 1 else 0),
    Combine = List.Transform(
                List.Zip(
                    {
                        Boolean,
                        List.RemoveFirstN(Boolean, 1) & {0},
                        {0} & List.RemoveLastN(Boolean, 1)
                    }
                ), each List.Max(_)
            ),
    AddToTable = Table.FromColumns(Table.ToColumns(#"Changed Type") & {Combine}, Table.ColumnNames(#"Changed Type") & {"Boolean"}),
    AddColumn3 = Table.FromRecords(Table.TransformRows(AddToTable, each _ & [#"Column 3" = if [Boolean] = 1 then [Column 1] else null])),
    #"Changed Type1" = Table.TransformColumnTypes(AddColumn3,{{"Column 1", Int64.Type}, {"Column 2", Int64.Type}, {"Boolean", Int64.Type}, {"Column 3", Int64.Type}})
in
    #"Changed Type1"