fix: handle H5Dataset missing fillvalue attribute with dtype-based fallback

docs/releases.md

@@ -1,5 +1,11 @@
 # Release notes
 
+## Unreleased
+
+### Bug Fixes
+
+HDFParser now includes a `_get_fill_value` function which wraps `dataset.fillvalue` in a try/except AttributeError.
+
 ## v2.6.1 (3rd May 2026)
 
 Adds end-to-end support for inlined chunk references in `ChunkManifest` (read via Kerchunk parsers, write via Kerchunk and Icechunk writers), plus Zarr-Python 3.2.0 compatibility and several bug fixes.

virtualizarr/parsers/hdf/hdf.py

@@ -40,7 +40,10 @@ def _get_fill_value(dataset: H5Dataset):
     Extract the fill value from an h5py dataset, handling string/bytes dtypes
     that don't return numpy scalars from dataset.fillvalue.
     """
-    raw = dataset.fillvalue
+    try:
+        raw = dataset.fillvalue
+    except RuntimeError:
+        return np.ma.default_fill_value(dataset.dtype)
     if isinstance(raw, bytes):
         return raw.decode("utf-8", errors="replace")
     elif isinstance(raw, str):

virtualizarr/tests/test_parsers/test_hdf/test_hdf.py

@@ -240,3 +240,20 @@ def test_netcdf_over_https():
     ):
         np.testing.assert_allclose(ds["z"].min().to_numpy(), -6)
         np.testing.assert_allclose(ds["z"].max().to_numpy(), 817)
+
+
+def test_fillvalue_runtime_error():
+    from virtualizarr.parsers.hdf.hdf import _get_fill_value
+
+    dtype = np.dtype("float32")
+
+    class _RuntimeErrorDataset:
+        @property
+        def fillvalue(self):
+            raise RuntimeError("Unable to get fill value")
+
+    dataset = _RuntimeErrorDataset()
+    dataset.dtype = dtype  # type: ignore[attr-defined]
+
+    result = _get_fill_value(dataset)
+    assert result == np.ma.default_fill_value(dtype)