state manager: Updating non-existed array element does nothing

src/DotVVM.Framework/Resources/Scripts/state-manager.ts

@@ -326,8 +326,12 @@ function createWrappedObservable<T>(initialValue: DeepReadonly<T>, typeHint: Typ
                     }
                     const indexForClosure = index
                     newContents[index] = createWrappedObservable(newVal[index], Array.isArray(typeHint) ? typeHint[0] : void 0, update => updater((viewModelArray: any) => {
-                        const newElement = update(viewModelArray![indexForClosure])
-                        const newArray = createArray(viewModelArray!)
+                        if (viewModelArray == null || viewModelArray.length <= indexForClosure) {
+                            // the item or the array does not exist anymore
+                            return viewModelArray
+                        }
+                        const newElement = update(viewModelArray[indexForClosure])
+                        const newArray = createArray(viewModelArray)
                         newArray[indexForClosure] = newElement
                         return Object.freeze(newArray) as any
                     }))

src/DotVVM.Framework/Resources/Scripts/tests/stateManagement.test.ts

@@ -438,3 +438,21 @@ test("push on observable array - automatic coercion happens", () => {
     expect(vm.Array()[2]).toEqual(oldValue);
 
 })
+
+test("update of element in array that stops existing", () => {
+
+    vm.Array([
+        { Id: 1 },
+        { Id: 3 }
+    ])
+    expect(vm.Array.state.length).toEqual(2)
+    const a = vm.Array()[1]()
+    a.Id(10)
+    expect(vm.Array.state[1].Id).toEqual(10)
+    vm.Array([ { Id: 1 } ])
+    expect(vm.Array.state.length).toEqual(1)
+    a.Id(10)
+    expect(vm.Array.state.length).toEqual(1)
+    expect(vm.Array.state[0]).toEqual({ $type: "t2", Id: 1 })
+
+})