Fix bug in v2 zarr parser which interprets empty dimension list as truthy (#936)

* fix empty list truthy bug

* Fix scalar variable parsing in ZarrParser

Fix `ZarrParser` issue with scalar variable parsing from v2 native zarr stores.

Author: jbusecke

docs/releases.md

@@ -40,6 +40,8 @@
 - Fix `ZarrParser` not using the store-relative path when the zarr store is nested inside the object store root
   ([#913](https://github.com/zarr-developers/VirtualiZarr/pull/913)).
   By [Tom Nicholas](https://github.com/TomNicholas).
+- Fix `ZarrParser` not correctly parsing scalar variables from v2 native zarr stores ([#936](https://github.com/zarr-developers/VirtualiZarr/pull/936)).
+  By [Julius Buseceke](https://github.com/jbusecke)
 
 ### Documentation
 

virtualizarr/parsers/zarr.py

@@ -348,7 +348,7 @@ def _convert_v2_to_v3_dict(metadata: ArrayV2Metadata) -> dict:
     # to V3's dimension_names, so we do it manually.
     attrs = cast(dict, v3_dict.get("attributes", {}))
     dim_names = attrs.get("_ARRAY_DIMENSIONS")
-    if v3_dict.get("dimension_names") is None and dim_names:
+    if v3_dict.get("dimension_names") is None and dim_names is not None:
         v3_dict["dimension_names"] = dim_names
 
     # _ARRAY_DIMENSIONS is a V2 convention that gets promoted to dimension_names in V3,

virtualizarr/tests/test_parsers/test_zarr.py

@@ -243,6 +243,17 @@ def test_v2_metadata_with_dimensions():
     assert metadata.dimension_names == ("x", "y")
 
 
+@requires_v2_migration
+def test_v2_metadata_with_scalar_dimensions():
+    """Test V2 metadata conversion for scalar array with _ARRAY_DIMENSIONS=[]."""
+    store = zarr.storage.MemoryStore()
+    array = zarr.create(shape=(), chunks=(), dtype="int64", store=store, zarr_format=2)
+    array.attrs["_ARRAY_DIMENSIONS"] = []
+
+    metadata = metadata_as_v3(zarr.open(store, mode="r").metadata)
+    assert metadata.dimension_names == ()
+
+
 def test_v3_metadata_separator_normalized():
     """Test that metadata_as_v3 normalizes V3 chunk_key_encoding separator to '.'."""
     store = zarr.storage.MemoryStore()