diff --git a/src/anomalib/data/base/dataset.py b/src/anomalib/data/base/dataset.py
index 3a4a14798a..6a306d4618 100644
--- a/src/anomalib/data/base/dataset.py
+++ b/src/anomalib/data/base/dataset.py
@@ -45,7 +45,7 @@ def __init__(self, task: TaskType, transform: A.Compose) -> None:
         super().__init__()
         self.task = task
         self.transform = transform
-        self._samples: DataFrame = None
+        self._samples: DataFrame
 
     def __len__(self) -> int:
         """Get length of the dataset."""
@@ -66,7 +66,7 @@ def subsample(self, indices: Sequence[int], inplace: bool = False) -> AnomalibDa
     @property
     def is_setup(self) -> bool:
         """Checks if setup() been called."""
-        return isinstance(self._samples, DataFrame)
+        return hasattr(self, "_samples")
 
     @property
     def samples(self) -> DataFrame: