diff --git a/.gitignore b/.gitignore
index 5c443473f..13eb8b573 100644
--- a/.gitignore
+++ b/.gitignore
@@ -167,3 +167,4 @@ cython_debug/
 # Test
 tests
 **/_future/*
+data/MNIST
\ No newline at end of file
diff --git a/src/evox/problems/neuroevolution/__init__.py b/src/evox/problems/neuroevolution/__init__.py
index 1429f6f79..e69de29bb 100644
--- a/src/evox/problems/neuroevolution/__init__.py
+++ b/src/evox/problems/neuroevolution/__init__.py
@@ -1,4 +0,0 @@
-__all__ = ["BraxProblem", "SupervisedLearningProblem"]
-
-from .brax import BraxProblem
-from .supervised_learning import SupervisedLearningProblem
diff --git a/src/evox/problems/neuroevolution/brax.py b/src/evox/problems/neuroevolution/brax.py
index 67210e8c0..9ae4fba2b 100644
--- a/src/evox/problems/neuroevolution/brax.py
+++ b/src/evox/problems/neuroevolution/brax.py
@@ -1,13 +1,26 @@
+__all__ = ["BraxProblem"]
+
 from typing import Callable, Dict, Tuple
 
 import jax
 import jax.numpy as jnp
 import torch
 import torch.nn as nn
+import torch.utils.dlpack
 from brax import envs
+from torch.utils.dlpack import from_dlpack, to_dlpack
 
 from ...core import Problem, jit_class
-from .utils import from_jax_array, get_vmap_model_state_forward, to_jax_array
+from .utils import get_vmap_model_state_forward
+
+
+def to_jax_array(x: torch.Tensor) -> jax.Array:
+    return jax.dlpack.from_dlpack(to_dlpack(x.detach()))
+
+
+def from_jax_array(x: jax.Array) -> torch.Tensor:
+    return from_dlpack(jax.dlpack.to_dlpack(x, take_ownership=True))
+
 
 __brax_data__: Dict[
     int,
@@ -113,7 +126,6 @@ def __init__(
     def __del__(self):
         global __brax_data__
         __brax_data__.pop(self._hash_id_, None)
-        super().__del__()
 
     def evaluate(self, pop_params: Dict[str, nn.Parameter]) -> torch.Tensor:
         """Evaluate the final rewards of a population (batch) of model parameters.
diff --git a/src/evox/problems/neuroevolution/supervised_learning.py b/src/evox/problems/neuroevolution/supervised_learning.py
index eb7459dfe..1b8ca9f0a 100644
--- a/src/evox/problems/neuroevolution/supervised_learning.py
+++ b/src/evox/problems/neuroevolution/supervised_learning.py
@@ -1,3 +1,5 @@
+__all__ = ["SupervisedLearningProblem"]
+
 from typing import Dict, Iterable, Iterator, Tuple
 
 import torch
@@ -122,7 +124,6 @@ def __init__(
     def __del__(self):
         global __supervised_data__
         __supervised_data__.pop(self._hash_id_, None)
-        super().__del__()
 
     @torch.jit.ignore
     def _data_loader_reset(self) -> None:
diff --git a/src/evox/problems/neuroevolution/utils.py b/src/evox/problems/neuroevolution/utils.py
index 2e81db5a0..1c552775e 100644
--- a/src/evox/problems/neuroevolution/utils.py
+++ b/src/evox/problems/neuroevolution/utils.py
@@ -2,11 +2,8 @@
 import types
 from typing import Any, Callable, Dict
 
-import jax
 import torch
 import torch.nn as nn
-import torch.utils.dlpack
-from torch.utils.dlpack import from_dlpack, to_dlpack
 
 from ...core import jit, use_state, vmap
 from ...core.module import assign_load_state_dict
@@ -87,11 +84,3 @@ def get_vmap_model_state_forward(
             param_to_state_key_map,
             model_buffers,
         )
-
-
-def to_jax_array(x: torch.Tensor) -> jax.Array:
-    return jax.dlpack.from_dlpack(to_dlpack(x.detach()))
-
-
-def from_jax_array(x: jax.Array) -> torch.Tensor:
-    return from_dlpack(jax.dlpack.to_dlpack(x, take_ownership=True))
diff --git a/unit_test/core/test_vmap_fix.py b/unit_test/core/test_vmap_fix.py
index 19e89d569..1410e02cd 100644
--- a/unit_test/core/test_vmap_fix.py
+++ b/unit_test/core/test_vmap_fix.py
@@ -51,7 +51,3 @@ def test_distance_fn_with_mask(self):
     def test_distance_fn_without_mask(self):
         distances = jit(distance_fn, trace=True, lazy=False, example_inputs=(self.costs,))
         self.assertIsNotNone(distances(self.costs))
-
-    def test_distance_fn_with_none(self):
-        distances = jit(distance_fn, trace=True, lazy=False, example_inputs=(self.costs, None))
-        self.assertIsNotNone(distances(self.costs, None))
diff --git a/unit_test/problems/test_brax.py b/unit_test/problems/test_brax.py
index 468f79e35..fcd11f10c 100644
--- a/unit_test/problems/test_brax.py
+++ b/unit_test/problems/test_brax.py
@@ -5,7 +5,7 @@
 import torch.nn as nn
 
 from evox.algorithms import PSO
-from evox.problems.neuroevolution import BraxProblem
+from evox.problems.neuroevolution.brax import BraxProblem
 from evox.utils import ParamsAndVector
 from evox.workflows import EvalMonitor, StdWorkflow
 
diff --git a/unit_test/problems/test_supervised_learning.py b/unit_test/problems/test_supervised_learning.py
index 03bdf38cf..40877ee29 100644
--- a/unit_test/problems/test_supervised_learning.py
+++ b/unit_test/problems/test_supervised_learning.py
@@ -9,7 +9,7 @@
 
 from evox.algorithms import PSO
 from evox.core import Algorithm, Parameter, jit_class
-from evox.problems.neuroevolution import SupervisedLearningProblem
+from evox.problems.neuroevolution.supervised_learning import SupervisedLearningProblem
 from evox.utils import ParamsAndVector
 from evox.workflows import EvalMonitor, StdWorkflow
 
diff --git a/unit_test/utils/test_jit_fix.py b/unit_test/utils/test_jit_fix.py
index 4171942dc..f24808e15 100644
--- a/unit_test/utils/test_jit_fix.py
+++ b/unit_test/utils/test_jit_fix.py
@@ -18,6 +18,6 @@ def test_basic_switch(self):
     def test_vmap_switch(self):
         x = torch.randint(low=0, high=10, size=(2, 10), dtype=torch.int)
         y = [torch.rand(2, 10) for _ in range(10)]
-        vmap_switch = jit(switch, trace=False)
+        vmap_switch = jit(switch, trace=False, lazy=True)
         z = vmap_switch(x, y)
         self.assertIsNotNone(z)