Insertion marker previewer throws with chameleon blocks

[BeksOmega]

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Description

See title

Reproduction steps

1. Open the test blocks in the playground.
2. Attach a chameleon block (there's a category called Chameleon) to a block with a next connection.
3. Disconnect them. Observe the error.

Stack trace

Uncaught Error: The insertion marker previewer tried to create a marker but the result is missing a connection. If you are using a mutator, make sure your domToMutation method is properly defined.
    at InsertionMarkerPreviewer.previewConnection (insertion_marker_previewer.ts:99:15)
    at BlockDragStrategy.updateConnectionPreview (block_drag_strategy.ts:261:31)
    at BlockDragStrategy.drag (block_drag_strategy.ts:213:10)
    at BlockSvg.drag (block_svg.ts:1639:23)
    at Dragger.moveDraggable (dragger.ts:71:20)
    at Dragger.onDrag (dragger.ts:41:10)
    at Gesture.updateIsDragging (gesture.ts:352:20)
    at Gesture.updateFromEvent (gesture.ts:224:12)
    at Gesture.handleMove (gesture.ts:501:12)
    at HTMLDocument.wrapFunc (browser_events.ts:65:9)

Screenshots

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Browsers

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