Quarkus Rest empty @QueryParam is handled differently

[ia3andy]

Describe the bug

I initially discovered this in code.quarkus unit tests. For example when using ?a= with a a List, the list size is not 0 while it was 1 before (with "") as content.

Same with String, before it was an empty string, not it's not defined.

Expected behavior

not sure but we need to clarify if it's an expected change

Actual behavior

it assumes ?a= is the same as ?

How to Reproduce?

reproducer-validation.zip

This reproducer works on 3.17

Output of uname -a or ver

No response

Output of java -version

No response

Quarkus version or git rev

main (3.18)

Build tool (ie. output of mvnw --version or gradlew --version)

No response

Additional information

No response

[ia3andy]

It seems the change is not in validation but in how the empty query param is treated
Before (in 3.17-), ?a= meant a="", in main it's the same as not having a
This makes the validation constraint fail since there is a default value.

I have another failing test on a similar case where ?e= and e is a list before it was a List.of("") and now it's a List.of().

[ia3andy]

THis started to fail on Nov 18 and was working on Nov 15

[ia3andy]

here is a new reproducer clearly showing that empty query params are now handled differently:

reproducer-empty-queryparam.zip

[quarkus-bot]

/cc @FroMage (rest), @stuartwdouglas (rest)

[FroMage]

This change was intentional, and explained in #42468 (comment)

If you have use-cases that require the old behaviour, let us know, because we could not think of any.

[geoand]

Thanks for spotting that @FroMage!

I had completely forgot about that one...

[ia3andy]

@FroMage let's close this when this is in the migraition guide

[ia3andy]

Thanks @FroMage @geoand @cescoffier