Allow to override a list/tuple in `base_config.Config` to empty list/tuple.

PiperOrigin-RevId: 342925872

official/modeling/hyperparams/base_config.py

@@ -182,6 +182,8 @@ class Config(params_dict.ParamsDict):
         self.__dict__[k] = self._import_config(v, subconfig_type)
       else:
         self.__dict__[k] = self._import_config(v, subconfig_type)
+    else:
+      self.__dict__[k] = self._import_config(v, subconfig_type)
 
   def __setattr__(self, k, v):
     if k not in self.RESERVED_ATTR:

official/modeling/hyperparams/base_config_test.py

@@ -347,6 +347,15 @@ class BaseConfigTest(parameterized.TestCase, tf.test.TestCase):
     self.assertIsInstance(config.y[1], DumpConfig4)
     self.assertSameElements(config.z, ['a', 'b', 'c'])
 
+  def test_override_by_empty_sequence(self):
+    config = DummyConfig5()
+    config.override({
+        'y': [],
+        'z': (),
+    }, is_strict=True)
+    self.assertEmpty(config.y)
+    self.assertEmpty(config.z)
+
 
 if __name__ == '__main__':
   tf.test.main()