I am creating a new copy of a report with a text column that is a combination of two fields (in my case text account ID, a pipe delimiter, and the month year in yyyy-mm format) to allow joining the two tables on two fields simultaniously.
when dragging one accountMonthYear column onto the other I got the error message: unable to get property 'value' of undefined or null reference. The first table showed rows of data, but the second, larger table was empty.
I found a workaround by dragging account number from one table to the other, the link dialog shows properly with both tables filled in. I then changed the selected columns to the ones I wanted to join on and it worked properly.