Combine Cell data when two neighboring cells are empty

My conundrum is this: I ran a pitvot table to organize three columns of data (email, name, brand). The resulting data can have more than one row of data in column 'C'. For example A1 has the email adress, B1 has the person's Name, and C1 has their first brand. A2 is blank, B2 is blank, but C2 has their second brand. This continues down the entire data set, with some entries havin many many brands in the C column. I'd like to combine the brands into the cell that relates to the email address and name. So C1, for example, would contain all the brands below it separated by a comma, until a new contact is present in column A. Any help would be appreciated!

Thanks! Here is a sample data set. Tab 1 is the example data, as described in my original post, with tab 2 being my desired results. As you can see from tab one, there is a varying amount of data in the brands column for each entry in email and contact. Any help would be much appreciated.


Data_set_example.xlsx

Mike! Thank you soo much! Upon a preliminary check after running your provided code, it seemed to have worked. Many, many thanks!