material grabber shows instance selection if the selected instance is missing

packs/BP/scripts/classes/Structure/StructureCollection.js

@@ -40,6 +40,10 @@ class StructureCollection {
         return structure;
     }
 
+    has(instanceName) {
+        return Boolean(this.structures[instanceName]);
+    }
+
     delete(instanceName) {
         const struct = this.get(instanceName);
         struct.delete();

packs/BP/scripts/options/materialGrabber.js

@@ -55,12 +55,11 @@ function onPlayerInteract(event) {
     const player = event.player;
     const target = event.block || event.target;
     const focusedInstanceName = Builders.get(player.id).materialInstanceName;
-    if (!focusedInstanceName) {
+    if (!focusedInstanceName || !structureCollection.has(focusedInstanceName))
         openInstanceSelectionForm(player, event);
-    } else {
+    else
         tryGrabMaterials(player, target, focusedInstanceName, event);
 }
-}
 
 function isActionItem(itemStack) {
     return itemStack?.typeId === 'construct:material_grabber';