REST: cannot add a reviewer using name/slug

Hi,
for '/rest/default-reviewers/1.0/projects/

{projectKey}

/condition' and POST I need to add a reviewer's ID and not name/slug.
So:
data = {sourceaMatcher:{}, targetMatcher:{}, reviewers:[

{id:3448}

]...} is OK,
while
data = {sourceaMatcher:{}, targetMatcher:{}, reviewers:[

{name:<user_name>}

]...} fails.
I do not think it's by design as I was able to user user names for other endpoints.

• BitBucket Server v 5.2.2
• error: Java NullPoiner (in server logs) and
  '
  Unknown macro: {"errors"}

  ' in REST response.

Regards,
Lukasz