magento2: Type Error occurred when creating object: Magento\Framework\Communication\Config\Data

Following the instructions on https://devdocs.magento.com/guides/v2.3/comp-mgr/cli/cli-upgrade.html for upgrading Magento, I got this error when executing the command “php bin/magento setup:upgrade”

Preconditions (*)

1. Upgraded from 2.2.3 -> 2.3.1
2. PHP Version 7.2.16

Steps to reproduce (*)

1. Starting with a 2.2.3 installation, in Magento root dir:
2. php bin/magento maintenance:enable
3. composer require magento/product-community-edition=2.3.1 --no-update
4. composer require --dev phpunit/phpunit:~6.2.0 friendsofphp/php-cs-fixer:~2.10.1 lusitanian/oauth:~0.8.10 pdepend/pdepend:2.5.2 sebastian/phpcpd:~3.0.0 squizlabs/php_codesniffer:3.2.2 --no-update
5. composer remove --dev sjparkinson/static-review fabpot/php-cs-fixer --no-update
6. Open composer.json and edit the “autoload”: “psr-4” section to include “Zend\Mvc\Controller\”: “setup/src/Zend/Mvc/Controller/”:

“autoload”: { “psr-4”: { “Magento\Framework\”: “lib/internal/Magento/Framework/”, “Magento\Setup\”: “setup/src/Magento/Setup/”, “Magento\”: “app/code/Magento/”, “Zend\Mvc\Controller\”: “setup/src/Zend/Mvc/Controller/” }, … } 6. composer create-project --repository=https://repo.magento.com magento/project-community-edition=2.3.1 temp_dir --no-install 7. rm -rf update 8. mv temp_dir/update . 9. rm -rf temp_dir 10. composer update 11. bin/magento cache:clean 12. rm -rf var/cache/* 13. rm -rf var/page_cache/* 14. rm -rf generated/code/* 15. bin/magento setup:upgrade

Expected result (*)

1. The command “bin/magento setup:upgrade” should finish without errors

Actual result (*)

1. The command “bin/magento setup:upgrade” breaks with message: Type Error occurred when creating object: Magento\Framework\Communication\Config\Data

In the system.log I see the whole message: [2019-05-07 13:47:47] main.CRITICAL: Type Error occurred when creating object: Magento\Framework\Communication\Config\Data, Argument 2 passed to Magento\Framework\Reflection\TypeProcessor::resolveFullyQualifiedClassName() must be of the type string, null given, called in /var/www/vhosts/schuhjaeger.at/magento2_test/shop-v2/vendor/magento/framework/Reflection/TypeProcessor.php on line 535 [] []

This is the function from TypeProcess.php:

` /** * Get the parameter type * * @param ParameterReflection $param * @return string * @throws \LogicException */ public function getParamType(ParameterReflection $param) { $type = $param->detectType(); if ($type === ‘null’) { throw new \LogicException(sprintf( ‘@param annotation is incorrect for the parameter “%s” in the method “%s:%s”.’ . ’ First declared type should not be null. E.g. string|null’, $param->getName(), $param->getDeclaringClass()->getName(), $param->getDeclaringFunction()->name )); } if ($type === ‘array’) { // try to determine class, if it’s array of objects $paramDocBlock = $this->getParamDocBlockTag($param); $paramTypes = $paramDocBlock->getTypes(); $paramType = array_shift($paramTypes);

        $paramType = $this->resolveFullyQualifiedClassName($param->getDeclaringClass(), $paramType);

        return strpos($paramType, '[]') !== false ? $paramType : "{$paramType}[]";
    }
    return $this->resolveFullyQualifiedClassName($param->getDeclaringClass(), $type);
}

`

According to the error message, the variable $type is null.

How can I solve this?

Thank you very much in advance!