Fix bug where a model with empty weights fails to load (tensorflow#7868)

* Fix bug where a model with empty weights fails to load

* Address linting complaints

---------

Co-authored-by: fengwuyao <131706622+fengwuyao@users.noreply.github.com>
Co-authored-by: Ping Yu <4018+pyu10055@users.noreply.github.com>

tfjs-layers/src/engine/container.ts

@@ -36,6 +36,17 @@ export interface ContainerArgs {
   name?: string;
 }
 
+// get weights key from tensor map in order to check if it is from keras v3.
+// e.g. dense/0
+const isKerasSavedModelFormat = (weights: NamedTensorMap): boolean => {
+  const keys = Object.keys(weights);
+  if (keys.length === 0) {
+    return false;
+  }
+  const key = keys[0].split('/');
+  return !isNaN(parseInt(key[key.length - 1], 10));
+};
+
 /**
  * A Container is a directed acyclic graph of layers.
  *
@@ -594,19 +605,16 @@ export abstract class Container extends Layer {
   loadWeights(weights: NamedTensorMap, strict = true) {
     const nameToWeight: {[name: string]: LayerVariable} = {};
     let totalWeightsCount = 0;
-    // get weights key from tensor map in order to check if it is from keras v3.
-    // e.g. dense/0
-    const key = Object.keys(weights)[0].split('/');
-    const isKerasSavedModelFormat = !isNaN(parseInt(key[key.length - 1], 10));
-    if (isKerasSavedModelFormat) {
+    const modelIsKerasSavedModelFormat = isKerasSavedModelFormat(weights);
+    if (modelIsKerasSavedModelFormat) {
       this.parseWeights(weights);
     }
     // Check if weights from keras v3.
     for (const layer of this.layers) {
       for (const [index, weight] of layer.weights.entries()) {
         // Parse the name to layerName/index.
         // e.g. dense/0, dense/1, dense_1/0, dense_1/1
-        const parsedName = isKerasSavedModelFormat ?
+        const parsedName = modelIsKerasSavedModelFormat ?
             `${weight.name.split('/').slice(0, -1).join('/') + '/'}${index}` :
             weight.originalName;
         if (nameToWeight[parsedName] != null) {

tfjs-layers/src/model_save_test.ts

@@ -140,6 +140,38 @@ describeMathCPUAndWebGL2('Save-load round trips', () => {
     }
   });
 
+  it('loadLayersModel: save and load a model with empty weights', async () => {
+    // https://github.com/tensorflow/tfjs/issues/7865
+    // Models without weights should still be valid models
+    const model1 = tfl.sequential();
+    model1.add(
+      tfl.layers.upSampling2d({
+        size: [2, 2],
+        dataFormat: 'channelsLast',
+        inputShape: [null, null, 3],
+      })
+    );
+
+    // Use a randomly generated model path to prevent collision.
+    const path = `testModel${new Date().getTime()}_${Math.random()}`;
+
+    // First save the model to local storage.
+    const modelURL = `localstorage://${path}`;
+    await model1.save(modelURL);
+    // Once the saving succeeds, load the model back.
+    const model2 = await tfl.loadLayersModel(modelURL);
+    // Verify that the topology of the model is correct.
+    expect(model2.toJSON(null, false)).toEqual(model1.toJSON(null, false));
+
+    // Check the equality of the two models' weights.
+    const weights1 = model1.getWeights();
+    const weights2 = model2.getWeights();
+    expect(weights2.length).toEqual(weights1.length);
+    for (let i = 0; i < weights1.length; ++i) {
+      expectTensorsClose(weights1[i], weights2[i]);
+    }
+  });
+
   it('Functional model, IndexedDB', async () => {
     const input = tfl.input({shape: [2, 2]});
     const layer1 = tfl.layers.flatten().apply(input);