Only check MediaPlaceholder allowedTypes array length if prop exists

[kadamwhite]

Description

Adds an existence check to allowedTypes before attempting to access allowedTypes.length to fix #11692.

How has this been tested?

• tested this patch against three custom blocks which utilize MediaPlaceholder without allowedTypes and confirmed that in all cases the patch allows these custom blocks to load as they did several weeks ago.
• introduced a basic unit test to catch the bug described in the issue

Types of changes

Bug fix: Add an undefined/null check to an array before accessing .length.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• N/A My code follows the accessibility standards.
• My code has proper inline documentation.

[ocean90]

You probably wanted to do this:

Suggested change

	const isOneType = 1 === allowedTypes && allowedTypes.length;
	const isOneType = allowedTypes && 1 === allowedTypes.length;

[ocean90]

What do you think about defining allowedTypes as an empty array by default?

[kadamwhite]

Right you are on the boolean 🤦‍♂️ And I considered initializing allowedTypes to [] in the destructuring assignment, but then backed off because we do a if ( ! this.props.allowedTypes ) check elsewhere. Upon reflection, since the default initialization won't mutate the value of the prop, the two approaches aren't incompatible and I think your suggestion's the way to go. Will push a commit momentarily.

[ocean90]

The check needs to stay :)

[kadamwhite]

🤦‍♂️

[kadamwhite]

@ocean90 Thanks for the review, apologies for the sloppy commits! Pushed up a fix, should be ready for review again once Travis has its say.

[youknowriad]

I see that the prop is also used in onlyAllowsImages and onlyAllowsImages methods, should we add the default values there too?

[kadamwhite]

I looked into that earlier, and I don't think changes are necessary in either of those cases. On onlyAllowsImages and onFilesUpload both, the existing logic should handle both [] and null/false/undefined/etc. (onlyAllowsImages has the checks in the media placeholder component, while onFilesUpload passes the prop value through to be checke within the mediaUpload method)