Nullable registered meta with format does not display in JSON schema

[chrisvanpatten]

When registering a piece of meta as a nullable type in the REST schema, it does not display in the JSON schema for the particular object.

For example, the following will not correctly register a meta key in REST:

<?php register_meta( 'post', 'backgroundColor', [ 'single' => true, 'type' => 'string', 'show_in_rest' => [ 'schema' => [ 'title' => __( 'Background Color' ), 'type' => [ 'string', 'null' ], 'format' => 'hex-color', ], ], ], ); 

The key will not be visible in the JSON schema, and the key/value pair will also not be available in the meta object in the post response from the API.