diff --git a/lerobot/common/datasets/abstract.py b/lerobot/common/datasets/abstract.py
index 3e0e2c32..e9613310 100644
--- a/lerobot/common/datasets/abstract.py
+++ b/lerobot/common/datasets/abstract.py
@@ -22,7 +22,7 @@ class AbstractExperienceReplay(TensorDictReplayBuffer):
         batch_size: int = None,
         *,
         shuffle: bool = True,
-        root: Path = None,
+        root: Path | None = None,
         pin_memory: bool = False,
         prefetch: int = None,
         sampler: SliceSampler = None,
@@ -32,7 +32,7 @@ class AbstractExperienceReplay(TensorDictReplayBuffer):
     ):
         self.dataset_id = dataset_id
         self.shuffle = shuffle
-        self.root = root if root is None else Path(root)
+        self.root = root
         storage = self._download_or_load_dataset()
 
         super().__init__(
diff --git a/lerobot/common/datasets/aloha.py b/lerobot/common/datasets/aloha.py
index 2ea4b831..52a5676e 100644
--- a/lerobot/common/datasets/aloha.py
+++ b/lerobot/common/datasets/aloha.py
@@ -87,7 +87,7 @@ class AlohaExperienceReplay(AbstractExperienceReplay):
         batch_size: int = None,
         *,
         shuffle: bool = True,
-        root: Path = None,
+        root: Path | None = None,
         pin_memory: bool = False,
         prefetch: int = None,
         sampler: SliceSampler = None,
diff --git a/lerobot/common/datasets/factory.py b/lerobot/common/datasets/factory.py
index 876b6a50..3f4772c4 100644
--- a/lerobot/common/datasets/factory.py
+++ b/lerobot/common/datasets/factory.py
@@ -1,13 +1,16 @@
 import logging
 import os
+from pathlib import Path
 
 import torch
 from torchrl.data.replay_buffers import PrioritizedSliceSampler, SliceSampler
 
 from lerobot.common.envs.transforms import NormalizeTransform, Prod
 
-# used for unit tests
-DATA_DIR = os.environ.get("DATA_DIR", None)
+# DATA_DIR specifies to location where datasets are loaded. By default, DATA_DIR is None and
+# we load from `$HOME/.cache/huggingface/hub/datasets`. For our unit tests, we set `DATA_DIR=tests/data`
+# to load a subset of our datasets for faster continuous integration.
+DATA_DIR = Path(os.environ["DATA_DIR"]) if "DATA_DIR" in os.environ else None
 
 
 def make_offline_buffer(
diff --git a/lerobot/common/datasets/pusht.py b/lerobot/common/datasets/pusht.py
index bac742d9..f4f6d9ac 100644
--- a/lerobot/common/datasets/pusht.py
+++ b/lerobot/common/datasets/pusht.py
@@ -90,7 +90,7 @@ class PushtExperienceReplay(AbstractExperienceReplay):
         batch_size: int = None,
         *,
         shuffle: bool = True,
-        root: Path = None,
+        root: Path | None = None,
         pin_memory: bool = False,
         prefetch: int = None,
         sampler: SliceSampler = None,
diff --git a/lerobot/common/datasets/simxarm.py b/lerobot/common/datasets/simxarm.py
index b4dd824f..7bcb03fb 100644
--- a/lerobot/common/datasets/simxarm.py
+++ b/lerobot/common/datasets/simxarm.py
@@ -43,7 +43,7 @@ class SimxarmExperienceReplay(AbstractExperienceReplay):
         batch_size: int = None,
         *,
         shuffle: bool = True,
-        root: Path = None,
+        root: Path | None = None,
         pin_memory: bool = False,
         prefetch: int = None,
         sampler: SliceSampler = None,