Latest Posts Widget Block throwing PHP warning

[ianbelanger79]

When the Latest Posts Widget Block is used, I am seeing a PHP warning in the editor for each instance of the block:

Notice: Undefined index: categories in /srv/www/wordpress-develop/public_html/build/wp-content/plugins/gutenberg/packages/block-library/src/latest-posts/index.php on line 22

This same error will also show on the frontend, if the Category of the block is set to "All".

To Reproduce

1. Create a post
2. Add the Latest Posts Widget Block
3. Set the category to "All"
4. See warning

Expected behavior
There shouldn't be any warnings

Screenshots

Desktop (please complete the following information):

• OS: Windows 10
• Browser Chrome
• Version 70.0.3538.102

Additional context

• Most recent version of GB Master, with all commits as of writing this
• GB Nightly build https://builds.danielbachhuber.com/gutenberg-nightly.zipdoes not throw any warnings

[dd32]

Duplicated with WordPress 4.9.8 + Gutenberg 4.5.

4.9.8 has this as $attributes:

wp-content/plugins/gutenberg/packages/block-library/src/latest-posts/index.php:16:
array (size=6)
  'postsToShow' => int 5
  'displayPostDate' => boolean false
  'postLayout' => string 'list' (length=4)
  'columns' => int 3
  'order' => string 'desc' (length=4)
  'orderBy' => string 'date' (length=4)

Where as 5.0 $attributes has this:

wp-includes/blocks/latest-posts.php:16:
array (size=9)
  'categories' => null
  'className' => null
  'postsToShow' => int 5
  'displayPostDate' => boolean true
  'postLayout' => string 'list' (length=4)
  'columns' => int 3
  'align' => null
  'order' => string 'desc' (length=4)
  'orderBy' => string 'date' (length=4)