Creating schema with type "null" for genres throws error on AWS Console for Amazon Personalize

Question

Using a web console for Amazon Personalize for creating item datasets, it throws an error "GENRES field cannot be of type null" when trying to create an item schema with GENRES that contains type "null". 
But the documentation https://docs.aws.amazon.com/personalize/latest/dg/how-it-works-dataset-schema.html has GENRES with type null for imperfect data. 
Also, it throws an error "schema is missing required field [genres]" if it's not included in the schema, which is odd, because the documentation says that the item schema requires ITEM_ID,  CREATION_TIMESTAMP, and 1 metadata field where the table doesn't even mention genres. https://docs.aws.amazon.com/personalize/latest/dg/custom-datasets-and-schemas.html#dataset-requirements

However, we could create the schema without genres when using the AWS SDK. Is this a bug in AWS console? or is it a new requirement that hasn't been updated on SDK?

Accepted Answer

Solved the issue, we were using "Video-On-Demand" instead of custom model, and the requirements were different.

Answer

If you are using a [Custom Dataset Group](https://docs.aws.amazon.com/personalize/latest/dg/custom-dataset-groups.html) you can define your own schema and allow for `null` values in a "GENRES" column: 
```
{
  "name": "GENRES",
  "type": [
    "null",
    "string"
  ],
  "categorical": true
}
```
There is no requirement to have a "GENRES" metadata field in [Custom Dataset Groups](https://docs.aws.amazon.com/personalize/latest/dg/custom-dataset-groups.html).

However, if you created a [Domain Dataset Group](https://docs.aws.amazon.com/personalize/latest/dg/domain-dataset-groups.html), for instance:

```
response = personalize.create_dataset_group( 
    name='personalize_vod_ds_group',
    domain='VIDEO_ON_DEMAND'
)
```
In the 'VIDEO_ON_DEMAND' domain "GENRES" is a required field ([Documentation](https://docs.aws.amazon.com/personalize/latest/dg/VIDEO-ON-DEMAND-datasets-and-schemas.html)) and will give an error if not provided.

Creating schema with type "null" for genres throws error on AWS Console for Amazon Personalize

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