Replace null values by random value from list using lookup in Power Query

UPDATE: I have found a working solution, as per below. Only difference is that I have to add as a new column because replacing in existing column using Table.TransformColumns function results in an 'Expression.Error: We cannot apply field access to the type Null.' error.

If anyone knows another (more elegant?) solution, feel free to share.

Bastiaan

let
    MainTable = Table.FromRecords({
        [Location = "N5", Section = null, Article = "S11127"], 
        [Location = "N5", Section = "", Article = "S11128"], 
        [Location = "N5", Section = "A4", Article = "S11129"], 
        [Location = "N5", Section = null, Article = "S11130"],
        [Location = "T22", Section = null, Article = "S11131"],
        [Location = "T22", Section = "", Article = "S11133"],
        [Location = "T22", Section = null, Article = "S11133"],
        [Location = "T22", Section = "2", Article = "S11134"]
        }),
    ReferenceTable = Table.FromRecords({
        [Location = "N5", Section = "A1"], 
        [Location = "N5", Section = "A2"],
        [Location = "N5", Section = "A3"],
        [Location = "N5", Section = "A4"],
        [Location = "N5", Section = "A5"],       
        [Location = "T22", Section = "1"],
        [Location = "T22", Section = "2"]
        }),
    
    RandomValue = (Row) =>
        let
            FilteredReferenceTable = Table.SelectRows(ReferenceTable, each [Location] = Row[Location]),
            RandomIndex = Number.RoundDown(Number.RandomBetween(0, Table.RowCount(FilteredReferenceTable))),
            SelectedValue = FilteredReferenceTable{RandomIndex}[Section]
        in
            SelectedValue,

    #"AddedCustom" = Table.AddColumn(MainTable, "Section NEW", each if [Section] = "" or [Section] = null then RandomValue(_) else [Section])
in
    #"AddedCustom"