I was wondering, what's the right way to implement an extensible EAV model.

I see that in `Magento\Catalog\Model\Product`, the method `getExtensionAttributes()` is implemented like this:

```
public function getExtensionAttributes()
{
    $extensionAttributes = $this->_getExtensionAttributes();
    if (!$extensionAttributes) {
        return $this->extensionAttributesFactory->create('Magento\Catalog\Api\Data\ProductInterface');
    }
    return $extensionAttributes;
}

```

But in others, like the customer or category models it's just

```
public function getExtensionAttributes()
{
    return $this->_getExtensionAttributes();
}

```

which can lead to a **NULL** result, if the **extension\_attributes** key has not been set before.

Pragmatically, I would prefer the first one. This way I can always be sure to get an instance of `Magento\Framework\Api\ExtensionAttributesInterface`, even if the model has just been instantiated.

But why is it not used in other modules then? Is it against the new separation of data models that we see in the customer module? If so, how are we supposed to initialize the extension attributes?