diff --git a/langfun/core/language_model.py b/langfun/core/language_model.py
index cf0d2d7..ee1448a 100644
--- a/langfun/core/language_model.py
+++ b/langfun/core/language_model.py
@@ -50,14 +50,6 @@ class LMSamplingResult(pg.Object):
       ),
   ] = []
 
-  error: Annotated[
-      Exception | None,
-      (
-          'Error information if sampling request failed. If Not None, '
-          '`samples` will be an empty list.'
-      ),
-  ] = None
-
 
 class LMSamplingOptions(component.Component):
   """Language model sampling options."""
@@ -200,14 +192,15 @@ def _sample_with_cache_lookup(
         results[i] = r.clone()
 
     # Sample non-cache-hit prompts.
-    requested_results = self._sample(requests)
-    assert len(requested_results) == len(requests), (
-        requests, requested_results)
+    if requests:
+      requested_results = self._sample(requests)
+      assert len(requested_results) == len(requests), (
+          requests, requested_results)
 
-    # Combine cached results and newly requested results.
-    for i, (prompt, result) in enumerate(zip(requests, requested_results)):
-      results[request_to_result_index[i]] = result
-      self.cache.put(self, prompt, result)
+      # Combine cached results and newly requested results.
+      for i, (prompt, result) in enumerate(zip(requests, requested_results)):
+        results[request_to_result_index[i]] = result
+        self.cache.put(self, prompt, result.clone())
 
     return results  # pytype: disable=bad-return-type
 
@@ -218,7 +211,10 @@ def _sample(
   ) -> list[LMSamplingResult]:
     """Subclass should override."""
 
-  def __call__(self, prompt: message_lib.Message, **kwargs) -> str:
+  def __call__(
+      self,
+      prompt: message_lib.Message,
+      **kwargs) -> message_lib.Message:
     """Returns the first candidate."""
     with component.context(override_attrs=True, **kwargs):
       sampling_options = self.sampling_options
@@ -252,7 +248,4 @@ def __call__(self, prompt: message_lib.Message, **kwargs) -> str:
             ),
             color='blue',
         )
-
-      if result.error:
-        raise result.error
       return response
diff --git a/langfun/core/language_model_test.py b/langfun/core/language_model_test.py
index 5e8c765..5249991 100644
--- a/langfun/core/language_model_test.py
+++ b/langfun/core/language_model_test.py
@@ -180,6 +180,18 @@ def test_using_cache(self):
     self.assertEqual(cache.cache_hit, 2)
     self.assertEqual(cache.num_records, 3)
 
+    lm = MockModel(cache=cache,
+                   top_k=1,
+                   failures_before_attempt=1,
+                   max_attempts=1)
+    try:
+      lm.sample(['a']),
+    except concurrent.RetryError:
+      pass
+
+    lm = MockModel(cache=cache, top_k=1)
+    self.assertEqual(lm('a'), 'a')
+
   def test_retry(self):
     lm = MockModel(
         failures_before_attempt=1, top_k=1,
diff --git a/langfun/core/llms/cache/in_memory.py b/langfun/core/llms/cache/in_memory.py
index 2d75bf9..fd784de 100644
--- a/langfun/core/llms/cache/in_memory.py
+++ b/langfun/core/llms/cache/in_memory.py
@@ -28,7 +28,8 @@ def _put(self, key: Any, entry: base.LMCacheEntry) -> None:
     """Puts a LM cache entry associated with the key."""
     _CACHE_MEMORY[key] = entry
 
-  def reset(self) -> None:
+  @classmethod
+  def reset(cls) -> None:
     """Resets the cache."""
     _CACHE_MEMORY.clear()
 
diff --git a/langfun/core/llms/cache/in_memory_test.py b/langfun/core/llms/cache/in_memory_test.py
index c340bc9..81b9672 100644
--- a/langfun/core/llms/cache/in_memory_test.py
+++ b/langfun/core/llms/cache/in_memory_test.py
@@ -23,7 +23,7 @@
 class InMemoryLMCacheTest(unittest.TestCase):
 
   def test_basics(self):
-    in_memory.InMemory().reset()
+    in_memory.InMemory.reset()
     lm = fake.StaticSequence(['1', '2', '3'], cache=in_memory.InMemory())
     self.assertEqual(lm('a'), '1')
     self.assertEqual(lm('a'), '1')
@@ -32,7 +32,7 @@ def test_basics(self):
     self.assertEqual(lm('c'), '3')
 
   def test_ttl(self):
-    in_memory.InMemory().reset()
+    in_memory.InMemory.reset()
     lm = fake.StaticSequence(['1', '2', '3'], cache=in_memory.InMemory(ttl=1))
     self.assertEqual(lm('a'), '1')
     self.assertEqual(lm('a'), '1')
@@ -40,7 +40,7 @@ def test_ttl(self):
     self.assertEqual(lm('a'), '2')
 
   def test_different_sampling_options(self):
-    in_memory.InMemory().reset()
+    in_memory.InMemory.reset()
     lm = fake.StaticSequence(['1', '2', '3'], cache=in_memory.InMemory())
     self.assertEqual(lm('a'), '1')
     self.assertEqual(lm('a'), '1')