feat: enhance Comfy API handling and add tests for branded non-Z diffusion models

core/layer-mask-utils.ts

@@ -2,6 +2,7 @@ import type { Layer } from "./layer";
 import type { LayerMask } from "./layer-mask";
 
 export function getLayerMask(layer: Layer | undefined): LayerMask | undefined {
+  if (!layer) return undefined;
   if (layer.layerMask) return layer.layerMask;
   if (!layer.clippingMask) return undefined;