Concatenate in MS Access - how to omit space and comma if first value is missing?
Thank you Akina for your suggestion.

As I am really a newbie, it took me some time to work out how to use IFF.

At the end here's the working string to remove comma and space at the beginning if the first value is null (empty):

=([Method].value) &amp; iif (IsNull([Method].value) ,"",", ") &amp; + [Experiment]