Guard against a null asset in `MuxMirrorFieldtype::preload() - #99

TLDR

This PR adds a null check in MuxMirrorFieldtype::preload() because depending on your data Statamic's $this->asset() can return null in certain circumstances, resulting in a Call to a member function isVideo() on null error. The fix is tiny and perfectly safe as far as I can tell.

Below is Claude's full explanation of the issue and how to reproduce it, if you really wanted to dig into it 🙂 .

Summary

MuxMirrorFieldtype::preload() calls $asset->isVideo() on a value that can be null, which throws a fatal error and returns a 500 for any control panel screen that builds the meta for an assets field whose container blueprint contains a mux_mirror field:

Call to a member function isVideo() on null
  at src/Fieldtypes/MuxMirrorFieldtype.php:60

In practice this takes down entry edit screens (and anywhere else an assets field is preloaded), not just the asset editor.

The fix

preload() already treats $asset as nullable on the line directly above ('is_asset' => (bool) $asset), but the next line dereferences it unconditionally:

return [
    'is_asset' => (bool) $asset,
    'is_video' => $asset->isVideo(),        // 💥 $asset can be null here
    ...
];

The one-line change mirrors the null handling already used for is_proxy:

-            'is_video' => $asset->isVideo(),
+            'is_video' => $asset?->isVideo() ?? false,

Root cause

MuxMirrorFieldtype::asset() returns null whenever the field's parent is not an Asset instance:

protected function asset(): ?Asset
{
    if ($this->field?->parent() instanceof Asset) {
        return $this->field->parent();
    }

    return null;
}

That happens during normal control panel usage because of how Statamic builds an asset's blueprint meta:

1. An assets field's preload() (Statamic\Fieldtypes\Assets\Assets) renders an inline preview of each selected asset via Statamic\Http\Resources\CP\Assets\AssetsFieldtypeAsset::publishFormData(), which builds the asset blueprint's field meta — including the mux_mirror field.
2. AssetContainer::blueprint($asset = null) returns a single, Blink-cached blueprint object and mutates its parent in place: setParent($asset ?? $this).
3. The same Assets::preload() also calls getColumns(), which calls $this->container()->blueprint() with no asset, setting that shared blueprint's parent to the container.
4. Because the blueprint object (and its built fields()) are cached and shared, a later asset preview ends up meta-ing the mux_mirror field with the AssetContainer as its parent instead of an Asset. asset() returns null, and $asset->isVideo() throws.

The underlying shared-mutable-blueprint behaviour is in Statamic core (present at least as far back as v5.74 / v6.0.0, so it is not a recent regression), but the addon is the thing that crashes on it. Guarding preload() makes the fieldtype resilient to being meta'd with a non-asset parent, which is the contract the rest of the method already assumes.

Reproduction

A minimal, isolated reproduction needs no Mux account, no API credentials and no mirrored video — just an image asset and the mux_mirror field on the container blueprint.

1. Fresh Statamic 6 site (reproduced on v6.23.0, PHP 8.5).

2. Add a mux_mirror field to the asset container blueprint (resources/blueprints/assets/assets.yaml):

   -
     handle: mux
     field:
       type: mux_mirror
       display: Mux

3. Give a collection two assets fields pointing at that container (image_one, image_two).

4. Upload one image and select the same asset in both fields on one entry.

5. Open that entry in the control panel → 500.

Why two fields / the same asset

Within Assets::preload(), getItemData() (the asset preview) runs before getColumns() (the call that poisons the shared blueprint), so a single field cannot crash its own preview. With two fields referencing the same asset:

• image_one previews the asset (caches its blueprint, parent = asset, fine), then its getColumns() poisons that cached blueprint (parent → container).
• image_two re-previews the same asset → cache hit on the now-poisoned blueprint → the mux_mirror field is meta'd with the container as parent → isVideo() on null → 500.

Impact

• Severity: any control panel edit screen that surfaces an assets field tied to a container with a mux_mirror field can 500. It can present as "every entry is broken" once content references such assets.
• Risk of the change: minimal — one expression, no behavioural change when $asset is a real asset; is_video simply becomes false when there is no asset, consistent with is_asset being false in the same payload.