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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@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.
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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>