Gutenberg: getEditedPostAttribute("meta") in Custom Post Type Returns Undefined

[conanliuhuan]

Describe the bug
I registered a custom posttype and set it "show in rest"
JS：wp.data.select( 'core/editor' ).getEditedPostAttribute('meta')
this returns undefied, it shoud always returns an Object.

To reproduce
Steps to reproduce the behavior:

1. register a posttype, PHP:
   register_post_type('my_posttype',array( 'labels' => array( 'name' => 'My PostType', ), 'public' => true, 'show_in_rest'=>true, ));
2. register a post meta, PHP:
   register_post_meta('my_posttype','meta_name',array( 'show_in_rest' => true, 'single' => true, 'type' => 'string', ));
3. Open My PostType / write new post
4. Browser Press F12 show console
5. type JS:
   wp.data.select( 'core/editor' ).getEditedPostAttribute('meta')
6. Press enter
7. return undefined

Expected behavior
JS : wp.data.select( 'core/editor' ).getEditedPostAttribute('meta')
Should returns a Object like:
{ meta_name: '' }

Screenshots

Desktop (please complete the following information):

• OS: Windows
• Browser Firefox
• Version 68.0.1

Smartphone (please complete the following information):

• Device:
• OS:
• Browser
• Version

Additional context

• Please add the version of Gutenberg you are using in the description.
  6.2.0
• To report a security issue, please visit the WordPress HackerOne program: https://hackerone.com/wordpress.

[conanliuhuan]

This BUG affects Custom Post Type Gutenberg Sidebar:

[conanliuhuan]

If custom post type wants to get meta in gutenberg, it have to support custom-fields when it register.

register_post_type('my_posttype',array( 'labels' => array( 'name' => 'My PostType', ), 'public' => true, 'supports' => [ 'title', 'editor', 'custom-fields', ], 'show_in_rest'=>true, ));

[raquelmv]

THANK YOU, took me 1 day of frustration to get here @conanliuhuan