Function joiner(rng As Range)
    Dim arr$(), tmp$
    Dim elem, c As New Collection
    
    joiner = ""
    If rng.Cells.Count <> 1 Then Exit Function
    
    tmp$ = Application.WorksheetFunction.Trim(rng.Value)
    arr$ = Split(tmp$, ",")
    
    On Error Resume Next
    For Each elem In arr
        c.Add Trim$(elem), Trim$(elem)
        If Err <> 0 Then
            Err.Clear
        ElseIf joiner <> "" Then
            joiner = joiner & ", " & Trim$(elem)
        Else
            joiner = elem
        End If
    Next elem
    On Error GoTo 0
    Set c = Nothing
    
End Function