Bug was introduced in commit 2a99b3d456
in an effort to get rid of partial List.tail,
because GHC-9.8 started to warn about it.
Problem is that the rewritten code with tailDef always removes the last account,
whereas the original intention was to replace all accounts by a comma except the last one.
addCommas should prepare a comma separated list like List.intercalate.
b74815287d