null input parameters custom function

Hi Mic1979 ,

Here is the complete Power Query M formula with the necessary modifications to handle null values properly in one code snippet:

(
    Input_Table as table,
    Adder_Table as table, 

    Input_Table_Column1 as text, Input_Table_Column2 as text, Input_Table_Column3 as text, Input_Table_Column4 as text, Input_Table_Column5 as text,

    Adder_Table_Column1 as text, Adder_Table_Column2 as text, Adder_Table_Column3 as text, Adder_Table_Column4 as text, Adder_Table_Column5 as text,

    Adder as text
) =>

let
    Input_Table_Helper_Column = Table.AddColumn(Input_Table, "HelperLPInput", each 
        Text.Combine(List.Select({
            Record.Field(_, Input_Table_Column1)?, 
            Record.Field(_, Input_Table_Column2)?, 
            Record.Field(_, Input_Table_Column3)?, 
            Record.Field(_, Input_Table_Column4)?, 
            Record.Field(_, Input_Table_Column5)?
        }, each _ <> null), " "), type text),

    Adder_Table_Helper_Column = Table.AddColumn(Adder_Table, "HelperLPAdder", each 
        Text.Combine(List.Select({
            Record.Field(_, Adder_Table_Column1)?, 
            Record.Field(_, Adder_Table_Column2)?, 
            Record.Field(_, Adder_Table_Column3)?, 
            Record.Field(_, Adder_Table_Column4)?, 
            Record.Field(_, Adder_Table_Column5)?
        }, each _ <> null), " "), type text),

    // Merge and Expand
    Merged_Table = Table.NestedJoin(
        Input_Table_Helper_Column,
        {"HelperLPInput"},
        Adder_Table_Helper_Column,
        {"HelperLPAdder"},
        "Adder",
        JoinKind.LeftOuter
    ),

    Input_Table_Headers = Table.ColumnNames(Input_Table),
    Adder_Table_Headers = Table.ColumnNames(Adder_Table),
    List_Header_Difference = List.Difference(Adder_Table_Headers, Input_Table_Headers),

    Expanded_Merged_Table = Table.ExpandTableColumn(
        Merged_Table,
        Adder,
        List_Header_Difference,
        List_Header_Difference
    ),

    Remove_HelperLPInput = Table.RemoveColumns(Expanded_Merged_Table, "HelperLPInput")

in 
    Remove_HelperLPInput

Key Fixes:
Handles null values properly using List.Select(..., each _ <> null), so Text.Combine doesn’t break.
Uses Record.Field(_, ColumnName)?, so missing fields don’t throw errors.
Removes null fields before concatenation, ensuring clean text output.
Now, your function should work perfectly even when passing null as an input parameter.  Let me know if you need any tweaks!

Best regards,