I still need to test well the priority, because it works on my symfony 5.0 (without it), but I want to try it on Symfony 4.4 to see if I have the same behavior.

I have 2 unit tests failing:

There were 2 errors:
1) Symfony\Component\Serializer\Tests\Normalizer\FlattenExceptionNormalizerTest::testNormalize with data set "instance from constructor" (Symfony\Component\ErrorHandler\Exception\FlattenException Object (...))
TypeError: Return value of Symfony\Component\ErrorHandler\Exception\FlattenException::getMessage() must be of the type string, null returned
/home/travis/build/symfony/symfony/src/Symfony/Component/ErrorHandler/Exception/FlattenException.php:190
/home/travis/build/symfony/symfony/src/Symfony/Component/Serializer/Normalizer/FlattenExceptionNormalizer.php:37
/home/travis/build/symfony/symfony/src/Symfony/Component/Serializer/Tests/Normalizer/FlattenExceptionNormalizerTest.php:46
2) Symfony\Component\Serializer\Tests\Normalizer\FlattenExceptionNormalizerTest::testDenormalizeValidData
TypeError: Return value of Symfony\Component\ErrorHandler\Exception\FlattenException::getMessage() must be of the type string, null returned
/home/travis/build/symfony/symfony/src/Symfony/Component/ErrorHandler/Exception/FlattenException.php:190
/home/travis/build/symfony/symfony/src/Symfony/Component/Serializer/Tests/Normalizer/FlattenExceptionNormalizerTest.php:93

@nicolas-grekas Maybe you can help me with this. I know that on the FlattenException Unit tests you never use the constructor without arguments.

You did the change in the past adding typehints to the FlattenException class methods, which makes total sense when you are creating this exception from throwable. But what can we do in this specific case?

Should I still use the empty constructor here or should I use reflection?

If I use it, makes sense to test the empty constructor but since they have different type hints from the getters (Example: message is null in the empty constructor, but getMessage() has a string typehint) the test fails.

Or should I follow the FlattenException unit tests and remove the empty constructor test?

Note: This does not happen in this specific feature, because the normalizer does not call any getter without a full FlattenException.

Tests need to be updated to pass.

@fabpot I have updated the tests but some Travis tests are failing with the error that the FlattenExceptionNormalizer class does not exist (FrameworkBundle is fetching v5.0 in Travis).

I suppose that will only be green when we merge this or am I missing something?

Thank you @monteiro.