Fix updateNodes not notifying when assigning

src/ObservableObject.ts

@@ -213,7 +213,7 @@ function updateNodes(parent: NodeValue, obj: Record<any, any> | Array<any> | und
         }
     }
 
-    if (obj && !isPrimitive(obj) && !parent.lazy) {
+    if (obj && !parent.lazy && !isPrimitive(obj)) {
         hasADiff = hasADiff || length !== lengthPrev;
         const isArrDiff = hasADiff;
         let didMove = false;
@@ -556,6 +556,12 @@ function setKey(node: NodeValue, key: string, newValue?: any, level?: number) {
     // Get the child node for updating and notifying
     const childNode: NodeValue = isRoot ? node : getChildNode(node, key);
 
+    if (childNode.lazy) {
+        // Make sure the node is activated when assigning because the node
+        // is never accessed through the proxy
+        peek(childNode);
+    }
+
     // Set the raw value on the parent object
     const { newValue: savedValue, prevValue, parentValue } = setNodeValue(childNode, newValue);
 

tests/tests.test.ts

@@ -511,6 +511,20 @@ describe('Listeners', () => {
             { path: ['test'], pathTypes: ['object'], valueAtPath: { test2: 'hi' }, prevAtPath: undefined },
         ]);
     });
+    test('Start undefined assign something', () => {
+        interface Data {
+            test?: undefined | { test2: string };
+        }
+        const obs = observable<Data>({});
+        const handler = expectChangeHandler(obs);
+
+        obs.assign({ test: { test2: 'hi' } });
+
+        // TODO: The previous value here is not totally correct because it filled out the path to make set work
+        expect(handler).toHaveBeenCalledWith({ test: { test2: 'hi' } }, { test: undefined }, [
+            { path: ['test'], pathTypes: ['object'], valueAtPath: { test2: 'hi' }, prevAtPath: undefined },
+        ]);
+    });
     test('Set with object should only fire listeners once', () => {
         interface Data {
             test: undefined | Record<string, string>;