M2.3.2 : Nullable getters in Service Contracts will throw a reflection error when used in the web API

[kanduvisla]

Preconditions

1. Magento 2.3.2 & 2.3-develop

Steps to reproduce

Create an interface with a nullable getter. In our scenario it was a method that could return an array of instances of another object, or null:

/**
 * @return null|\Vendor\Module\Api\Data\CompanyAddressInterface[]
 */
public function getAddresses(): ?array;

Expected result

When properly configured and used as a web API, the object should be serialized using Reflection and it's nested objects as well.

Actual result

The following error is thrown:

Possible cause

My guess is that when determinating the type of return class, something goes wrong when a return type can be nullable. See also the workaround:

Workaround

The current woraround that will not trigger this error and make the web API work as expected is to flip the arguments, so instead of:

/**
 * @return null|\Vendor\Module\Api\Data\CompanyAddressInterface[]
 */
public function getAddresses(): ?array;

I use:

/**
 * @return \Vendor\Module\Api\Data\CompanyAddressInterface[]|null
 */
public function getAddresses(): ?array;

Now everything works as expected, but it seems to me that this should be considered a bug.

[m2-assistant]

Hi @kanduvisla. Thank you for your report.
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Please make sure that the issue is reproducible on the vanilla Magento instance following Steps to reproduce. To deploy vanilla Magento instance on our environment, please, add a comment to the issue:

@magento give me 2.3-develop instance - upcoming 2.3.x release

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@kanduvisla do you confirm that you were able to reproduce the issue on vanilla Magento instance following steps to reproduce?

• yes
• no

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[m2-assistant]

Hi @engcom-Charlie. Thank you for working on this issue.
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[magento-engcom-team]

✅ Confirmed by @engcom-Charlie
Thank you for verifying the issue. Based on the provided information internal tickets MC-29037 were created

Issue Available: @engcom-Charlie, You will be automatically unassigned. Contributors/Maintainers can claim this issue to continue. To reclaim and continue work, reassign the ticket to yourself.

[m2-assistant]

Hi @Parakoopa. Thank you for working on this issue.
Looks like this issue is already verified and confirmed. But if you want to validate it one more time, please, go though the following instruction:

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  Details

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[theCapypara]

A related issue, which must also be fixed:
When generating the swagger schema, Magento fails, if null is the first type in the @return annotation:

<response>
<message>
The "" data type isn't declared. Verify the type and try again.
</message>
<trace>
#0 /src/app/code/Magento/Webapi/Model/Rest/Swagger/Generator.php(471): Magento\Framework\Reflection\TypeProcessor->getTypeData('') #1 /src/app/code/Magento/Webapi/Model/Rest/Swagger/Generator.php(449): Magento\Webapi\Model\Rest\Swagger\Generator->generateDefinition('') #2 /src/app/code/Magento/Webapi/Model/Rest/Swagger/Generator.php(476): Magento\Webapi\Model\Rest\Swagger\Generator->getObjectSchema(NULL, '') #3 /src/app/code/Magento/Webapi/Model/Rest/Swagger/Generator.php(449): Magento\Webapi\Model\Rest\Swagger\Generator->generateDefinition('TudockTestDataT...') #4 /src/app/code/Magento/Webapi/Model/Rest/Swagger/Generator.php(910): Magento\Webapi\Model\Rest\Swagger\Generator->getObjectSchema('TudockTestDataT...', '') #5 /src/app/code/Magento/Webapi/Model/Rest/Swagger/Generator.php(271): Magento\Webapi\Model\Rest\Swagger\Generator->generateMethodSuccessResponse(Array, Array) #6 /src/app/code/Magento/Webapi/Model/Rest/Swagger/Generator.php(252): Magento\Webapi\Model\Rest\Swagger\Generator->generateMethodResponses(Array) #7 /src/app/code/Magento/Webapi/Model/Rest/Swagger/Generator.php(170): Magento\Webapi\Model\Rest\Swagger\Generator->generatePathInfo('get', Array, 'tudockTestV1') #8 /src/app/code/Magento/Webapi/Model/AbstractSchemaGenerator.php(109): Magento\Webapi\Model\Rest\Swagger\Generator->generateSchema(Array, 'https', 'magento-github....', '/rest/all/schem...') #9 /src/app/code/Magento/Webapi/Controller/Rest/SchemaRequestProcessor.php(59): Magento\Webapi\Model\AbstractSchemaGenerator->generate(Array, 'https', 'magento-github....', '/rest/all/schem...') #10 /src/app/code/Magento/Webapi/Controller/Rest.php(188): Magento\Webapi\Controller\Rest\SchemaRequestProcessor->process(Object(Magento\Framework\Webapi\Rest\Request\Proxy)) #11 /src/lib/internal/Magento/Framework/Interception/Interceptor.php(58): Magento\Webapi\Controller\Rest->dispatch(Object(Magento\Framework\App\Request\Http)) #12 /src/lib/internal/Magento/Framework/Interception/Interceptor.php(138): Magento\Webapi\Controller\Rest\Interceptor->___callParent('dispatch', Array) #13 /src/lib/internal/Magento/Framework/Interception/Interceptor.php(153): Magento\Webapi\Controller\Rest\Interceptor->Magento\Framework\Interception\{closure}(Object(Magento\Framework\App\Request\Http)) #14 /src/generated/code/Magento/Webapi/Controller/Rest/Interceptor.php(26): Magento\Webapi\Controller\Rest\Interceptor->___callPlugins('dispatch', Array, Array) #15 /src/lib/internal/Magento/Framework/App/Http.php(116): Magento\Webapi\Controller\Rest\Interceptor->dispatch(Object(Magento\Framework\App\Request\Http)) #16 /src/generated/code/Magento/Framework/App/Http/Interceptor.php(24): Magento\Framework\App\Http->launch() #17 /src/lib/internal/Magento/Framework/App/Bootstrap.php(260): Magento\Framework\App\Http\Interceptor->launch() #18 /src/pub/index.php(40): Magento\Framework\App\Bootstrap->run(Object(Magento\Framework\App\Http\Interceptor)) #19 {main}
</trace>
</response>

[magento-engcom-team]

Hi @kanduvisla. Thank you for your report.
The issue has been fixed in #25806 by @Parakoopa in 2.4-develop branch
Related commit(s):

• 0cea191adfc16bb7b3fcfc5b0d331bf3420ecc5d
• 99a1a98228b4dc0e280ad9d3feec89f6d2ecb334
• 253f881cb1c4b8ca1a8d8a94d939f9b76f1cd6b2
• 7e3390dd86faf45018a18e5f76d0ebe067019186

The fix will be available with the upcoming 2.4.0 release.