Raise error if quantizing non built model.

PiperOrigin-RevId: 257695954

Author: nutsiepully

tensorflow_model_optimization/python/core/quantization/keras/quantize_emulate.py

@@ -172,6 +172,11 @@ def quantize_apply(model):
                      'annotated with `quantize_annotate`. There are no layers '
                      'to quantize.')
 
+  if not model.built:
+    raise ValueError('quantization cannot be applied to a model which has not'
+                     'been built yet. Please call `model.build(input_shape)`'
+                     'before quantizing your model.')
+
   def _clone_model_with_weights(model_to_clone):
     cloned_model = keras.models.clone_model(model_to_clone)
     cloned_model.set_weights(model_to_clone.get_weights())

tensorflow_model_optimization/python/core/quantization/keras/quantize_emulate_test.py

@@ -179,6 +179,14 @@ def testRaisesErrorNoAnnotatedLayers_Functional(self):
     with self.assertRaises(ValueError):
       quantize_emulate.quantize_apply(model)
 
+  def testRaisesErrorModelNotBuilt(self):
+    model = keras.Sequential([
+        quantize_annotate(keras.layers.Dense(10), **self.quant_params1)])
+
+    self.assertFalse(model.built)
+    with self.assertRaises(ValueError):
+      quantize_emulate.quantize_apply(model)
+
   # Quantization Apply Tests
 
   def _get_annotated_sequential_model(self):