Fix rest tests

I went trough the core commit-log and I can't see anything committed in the last 5 days that could've caused this. I think.

I tried debugging this with git bisect on drupal core 8.3. I had a green test when I ran this on my local machine.

So I started by updating drupal core. I ran the test again and got a red test.

87da4d0..4f6dc7b 8.3.x -> origin/8.3.x

I started by running: git bisect start HEAD 87da4d0 - to indicate to git bisect that HEAD's broken and it worked on my previous checkout (87da4d0).
So I reran the test and typed git bisect good when it was green, git bisect bad when it was red. That left me with a green test on bc7dcc916e564a1d8400f5878ccd0e69eba16e89.

so then I typed git log 182f8fd18b55ccbeb000b9219f6709840031e628..HEAD and scrolled down to the bottom, the first commit was 3a8b4eee946f6e8905456f03ee5dd91fc0fb4a56. I did a git checkout of that (git checkout 3a8b4eee946f6e8905456f03ee5dd91fc0fb4a56 and reran the test, that gave me a red test (as expected).

It looks like the change was introcuded in http://cgit.drupalcode.org/drupal/commit/?h=8.3.x&id=3a8b4eee946f6e89054...

Command used for testing: php core/scripts/run-tests.sh --verbose --color --browser --concurrency 4 --php `which php` --url http://localhost/search-drupal --class '\Drupal\rest_facets\Tests\RestIntegrationTest::testRestResults'

Now to figure out why this broke that test and specificially why this introduced: Value 'http://localhost/checkout/facets-rest?' is equal to value 'http://localhost/checkout/facets-rest'..

I'll try to figure this out

This is a quickfix, but shouldn't be the thing that we commit - I feel.

This is a fix of the actual problem. Looks like drupal core no longer allows to have something empty passed into the query options ($url->setOption('query', ...).

Committed.