fix image insert console error

[vladanost]

Description

Fixes #3633

Editable component is complaining about the caption value type.
On new Image its an empty string and Editable expects an array (caption is registered as type array) or undefined so I set it to undefined if empty string.

I tried setting a default value when registering block type to empty array but that does not work.

caption: {
    type: 'array',
    source: 'children',
    selector: 'figcaption',
    default: [],
},

I would also assume that since caption is registered as type array that default value would be empty array. But I guess it doesn't work that way.

How Has This Been Tested?

Manually tested in the browser.
Current js unit tests pass.

[youknowriad]

Thanks for catching this bug,

I investigated a bit and I think the issue we have is elsewhere. When we select an image from the media library, we copy it's caption and it's always a string, we should not copy the caption if it's empty and we should wrap it in an array if it's not empty.

See the onSelectImage function in the image block.

[vladanost]

@youknowriad Thanks. Your suggestion seems to work.

[codecov]

Codecov Report

Merging #3634 into master will decrease coverage by 0.05%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #3634      +/-   ##
==========================================
- Coverage   36.95%   36.89%   -0.06%     
==========================================
  Files         268      275       +7     
  Lines        6673     6632      -41     
  Branches     1202     1202              
==========================================
- Hits         2466     2447      -19     
+ Misses       3555     3532      -23     
- Partials      652      653       +1

Impacted Files	Coverage Δ
blocks/library/image/block.js	1.72% <0%> (-0.1%)	⬇️
editor/reducer.js	90% <0%> (-0.28%)	⬇️
editor/selectors.js	92.85% <0%> (-0.27%)	⬇️
.../edit-post/sidebar/document-outline-panel/index.js	0% <0%> (ø)	⬆️
editor/edit-post/modes/visual-editor/index.js	0% <0%> (ø)	⬆️
editor/edit-post/layout/index.js	0% <0%> (ø)	⬆️
editor/edit-post/sidebar/post-trash/index.js	0% <0%> (ø)	⬆️
editor/edit-post/header/header-toolbar/index.js	0% <0%> (ø)	⬆️
editor/components/block-list/index.js	0% <0%> (ø)	⬆️
editor/edit-post/header/index.js	0% <0%> (ø)	⬆️
... and 17 more

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[youknowriad]

Nice Thanks