fix #17582 ./bin/magento config:show fails with a fatal error

[keyurshah070]

Description

Fixed Issues (if relevant)

1. ./bin/magento config:show fails with a fatal error #17582: ./bin/magento config:show fails with a fatal error

Manual testing scenarios

1. Fork fresh Magento from GitHub

2. Install and configure Magento 2

3. Run the first command php bin/magento config:dump to dump the configuration value

4. show the config dump php bin/magento config:show (Now it shows correctly the value rather then PHP fatel error) (please check attached file show.txt)
   show.txt

5. Run the php unit test

$ php vendor/bin/phpunit -c dev/tests/unit/phpunit.xml.dist app/code/Magento/Config
PHPUnit 6.2.4 by Sebastian Bergmann and contributors.

............................................................... 63 / 395 ( 15%)
............................................................... 126 / 395 ( 31%)
............................................................... 189 / 395 ( 47%)
............................................................... 252 / 395 ( 63%)
............................................................... 315 / 395 ( 79%)
............................................................... 378 / 395 ( 95%)
................. 395 / 395 (100%)

Time: 855 ms, Memory: 28.00MB

OK (395 tests, 1181 assertions)

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-cicd2]

All committers have signed the CLA.

[magento-engcom-team]

Hi @keyurshah070. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

• @magento-engcom-team give me test instance - deploy test instance based on PR changes
• @magento-engcom-team give me {$VERSION} instance - deploy vanilla Magento instance

For more details, please, review the Magento Contributor Assistant documentation

[magento-engcom-team]

Hi @keyurshah070. Thank you for your contribution.
We will aim to release these changes as part of 2.2.8.
Please check the release notes for final confirmation.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.