URLrewriter 'Append Query String' doesn't add a ? to the start of the query strings.

'Append Query String' doesn't add a ? to the start of the query strings.

Reproduction path:
Add a rule with document type 'Advanced Rule'.

Tick the box of 'Use Wildcard Matching'.
Tick the box of 'Append Query String'.
Rewrite From:
/bla/abc/something
Rewrite To:
/bla

Test URL: /bla/abc/something?query=string

Expected rewrite result: /bla?query=string

Actual result: /bla&query=string

Workaround; Make the 'Rewrite To' as: /bla?a=a