[PHP] ArrayAccess methods in Models missing return types

[AlexSBlackburn]

Description

Swagger Client Models implement the ArrayAccess interface and use the offset methods (offsetExists(), offsetGet(), offsetSet() and offsetUnset()). These methods are missing return types, causing warnings to be generated.

For example:
Return type of Swagger\Client\{ClientName}\Model\{ModelName}::offsetUnset($offset) should either be compatible with ArrayAccess::offsetUnset(mixed $offset): void, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /var/www/html/vendor/{vendor-name}/{package-name}/lib/Model/{ModelName}.php on line 330

Swagger-codegen version

3.0.34

Suggest a fix/enhancement

Add return types to the method declarations in https://github.com/swagger-api/swagger-codegen/blob/master/modules/swagger-codegen/src/main/resources/php/model_generic.mustache#L397