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Reproducible Example

left = pd.Series([None], dtype="date32[pyarrow]") right = pd.Series([None], dtype="null[pyarrow]") result = pd.concat([left, right]) >>> result.dtype timestamp[ms][pyarrow]

Issue Description

In ArrowDtype._get_common_dtype we go through

 new_dtype = find_common_type( [ dtype.numpy_dtype if isinstance(dtype, ArrowDtype) else dtype for dtype in dtypes if dtype != null_dtype ] ) 

The date dtype.numpy_dtype gives "M8[ms]", so we get new_dtype="M8[ms]", which gets cast to timestamp[ms][pyarrow].

Expected Behavior

date32[pyarrow]

Installed Versions