Convert a column with both text and table rows into text and combined text string

use Value.Is to find out what the data type of the cell is, and then handle the contents accordingly.

I ended up on this solution. 🙂 

#"Add new column and convert to list" = Table.AddColumn(#"Last step", "Name new column",
each if Value.Type([name original column]) = Value.Type("text") then [name original column]
else Table.ToList([name original column])),

#"Convert list to string" = Table.TransformColumns(#"Add new column and convert to list", {"Name new column",
each if Value.Type(_) = Value.Type("text") then _
else Text.Combine(List.Transform(_, Text.From), ","), type text}),

#"Remove old column" = Table.RemoveColumns(#"Convert list to string",{"name original column"})