Ensure that url suffix resolvers return strings to match function declaration

[aligent-lturner]

Description (*)

This pull request is to fix #30909 - where a null value for the product and/or category url suffix results in a type error being thrown during GraphQL queries

Fixed Issues (if relevant)

1. Fixes ProductUrlSuffix and CategoryUrlSuffix GraphQL resolvers fail with null values #30909

Manual testing scenarios (*)

1. Clear product and category url suffix values in admin and save
2. Run GraphQL query that requests product and/or category url suffix value

Questions or comments

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 are green)

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[aligent-lturner]

@magento run all tests

[engcom-Alfa]

✔️ QA Passed

Manual testing scenario:

1. Go to Admin -> Stores -> Configuration -> Catalog -> Catalog -> Search Engine Optimization
2. Clear product and category url suffix values in admin and save

Run GraphQL query that requests product and/or category url suffix value

For Categories:

{
  categoryList {
    url_suffix
  }
}

Before: ✖️ Query fails

✖️ with the following error in exception.log:

2020-11-20 13:29:04] main.ERROR: Return value of Magento\CatalogUrlRewriteGraphQl\Model\Resolver\CategoryUrlSuffix::getCategoryUrlSuffix() must be of the type string, null returned {"exception":"[object] (GraphQL\\Error\\Error(code: 0): Return value of Magento\\CatalogUrlRewriteGraphQl\\Model\\Resolver\\CategoryUrlSuffix::getCategoryUrlSuffix() must be of the type string, null returned at /var/www/html/magento24/vendor/webonyx/graphql-php/src/Error/Error.php:174, TypeError(code: 0): Return value of Magento\\CatalogUrlRewriteGraphQl\\Model\\Resolver\\CategoryUrlSuffix::getCategoryUrlSuffix() must be of the type string, null returned at /var/www/html/magento24/app/code/Magento/CatalogUrlRewriteGraphQl/Model/Resolver/CategoryUrlSuffix.php:80)"} []

After: ✔️ Empty string(' ')is returned for url_suffix value

It was also checked when the product and category url suffix values were filled

Actual Result: ✔️ The correct value is returned for url_suffix

For Products:

Run GraphQL query that requests product and/or category url suffix value

{
 products(filter: {sku: {in: ["Simple 1"]}}, sort: {name: ASC}) {
    items {
      url_suffix}
}
}

Before: ✖️ Query fails

✖️ with the following error in exception.log:

[2020-11-20 14:07:10] main.ERROR: Return value of Magento\CatalogUrlRewriteGraphQl\Model\Resolver\ProductUrlSuffix::getProductUrlSuffix() must be of the type string, null returned {"exception":"[object] (GraphQL\\Error\\Error(code: 0): Return value of Magento\\CatalogUrlRewriteGraphQl\\Model\\Resolver\\ProductUrlSuffix::getProductUrlSuffix() must be of the type string, null returned at /var/www/html/magento24/vendor/webonyx/graphql-php/src/Error/Error.php:174, TypeError(code: 0): Return value of Magento\\CatalogUrlRewriteGraphQl\\Model\\Resolver\\ProductUrlSuffix::getProductUrlSuffix() must be of the type string, null returned at /var/www/html/magento24/app/code/Magento/CatalogUrlRewriteGraphQl/Model/Resolver/ProductUrlSuffix.php:80)"} []
After: ✔️ Empty string(' ')is returned for url_suffix value

[engcom-Charlie]

@magento run all tests

[engcom-Charlie]

@magento run Integration Tests, Functional Tests B2B

[aligent-lturner]

@magento run Functional Tests B2B

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