Biblatex-apa style is missing a comma in the text-citations. why?

Biblatex-apa style is missing a comma in the text-citations. why?

i have a follow up question to a previously answered one regarding commas
in citations and references:

Biblatex-apa style is missing a comma in the references. why?

it works for me in the reference section, but as a text-citation, there is
still a comma missing. according to APA 6th, there should be also a comma
in front of the "&" when 3 or more authors are used.
like this:
(Tom, Jerry, & Donald, 2012).
right now it looks like this:
(Tom, Jerry & Donald, 2012).
How can i fix it?