[fix] make legacy bnb code work (#37331)

* [fix] make legacy bnb code work

* [fix] use get with default instead of getter

* add test for bnb 8bit optim skip embed

* [fix] style

* add require annotation of bnb

---------

Co-authored-by: jaycha <jaycha@ncsoft.com>
Co-authored-by: Marc Sun <57196510+SunMarc@users.noreply.github.com>

tests/trainer/test_trainer.py

@@ -5962,3 +5962,22 @@ class OptimizerAndModelInspectionTest(unittest.TestCase):
             param = next(model.parameters())
             group = trainer.get_optimizer_group(param)
             self.assertIn(param, group["params"])
+
+    @require_bitsandbytes
+    def test_bnb_8bit_optimizer_skip_embedding(self):
+        model = BasicTextGenerationModel(8, 4)
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            for name_optim in ["rmsprop_bnb_8bit", "adamw_8bit"]:
+                args = TrainingArguments(
+                    output_dir=tmp_dir,
+                    report_to="none",
+                    optim=name_optim,
+                )
+                trainer = Trainer(model=model, args=args)
+                optimizer = trainer.create_optimizer()
+                modules = optimizer.mng.module_weight_config_triple
+                self.assertNotEqual(len(modules), 0)
+                module, name, config = modules[0]
+                self.assertIsInstance(module, torch.nn.Embedding)
+                self.assertEqual(name, "weight")
+                self.assertDictEqual(config, {"optim_bits": 32})