Doctrine orm left join bug reproduction

Thank you for taking the time to investigate my bug reproduction!

Please do the following:

make dev-build
make dev-start
make sh
bin/console doctrine:migrations:migrate # if missing symfony/runtime is reported, just wait a couple of seconds, the entrypoint still doing its job
bin/console app:create-test-data

Now the tests:

bin/console app:test:successful
# outputs correctly one row - entity Other named Test 1
bin/console app:test:failing
# should output one row - entity Other named Test 2 - but outputs nothing

If the leftJoin() in \App\Command\TestCommandTrait::preloadOthers() is changed to innerJoin(), it works as expected.

The reason is in \Doctrine\ORM\Internal\Hydration\ObjectHydrator::hydrateRowData() on the line if (isset($this->existingCollections[$collKey])) { :

In the failing scenario, the if is evaluated as true and the code then continues to the line unset($this->resultPointers[$dqlAlias]);.

For the successful test scenario, the if is evaluated as false and the code proceeds to $element = $this->getEntity($data, $dqlAlias);, even though the next hydrateRowData() call receives the proper row data for "Test 2" in $rowData = $this->gatherRowData($row, $id, $nonemptyComponents);