fix bugs, refine structured data type json representation

Author: d-v-b

src/zarr/core/array.py

@@ -192,7 +192,7 @@ class from that dict. If the input is a metadata object, return it.
     """
 
     if isinstance(data, ArrayMetadata):
-        raise
+        return data
     else:
         zarr_format = data["zarr_format"]
         if zarr_format == 3:

src/zarr/core/common.py

@@ -139,7 +139,7 @@ class GroupMetadataJSON_V3(TypedDict):
     zarr_format: Literal[3]
     node_type: Literal["group"]
     attributes: NotRequired[Mapping[str, JSON]]
-    consolidated_metadata: NotRequired[ConsolidatedMetadata_JSON_V3]
+    consolidated_metadata: NotRequired[ConsolidatedMetadata_JSON_V3 | None]
 
 
 # TODO: use just 1 generic class and parametrize the type of the value type of the metadata

src/zarr/core/dtype/npy/structured.py

@@ -6,7 +6,7 @@
 
 import numpy as np
 
-from zarr.core.common import NamedRequiredConfig, StructuredName_V2
+from zarr.core.common import NamedConfig, NamedRequiredConfig, StructuredName_V2
 from zarr.core.dtype.common import (
     DataTypeValidationError,
     DTypeConfig_V2,
@@ -56,7 +56,10 @@ class StructuredJSON_V2(DTypeConfig_V2[StructuredName_V2, None]):
 
 
 class StructuredJSON_V3(
-    NamedRequiredConfig[Literal["structured"], Mapping[str, Sequence[Sequence[str | DTypeJSON]]]]
+    NamedRequiredConfig[
+        Literal["structured"],
+        Mapping[str, Sequence[list[str | NamedConfig[str, Mapping[str, object]]]]],
+    ]
 ):
     """
     A JSON representation of a structured data type in Zarr V3.

src/zarr/core/group.py

@@ -418,7 +418,7 @@ def from_dict(cls, data: GroupMetadataJSON_V2 | GroupMetadataJSON_V3) -> GroupMe
         """
         Create an instance of GroupMetadata from a dict model of Zarr group metadata.
         """
-        if "consolidated_metadata" in data:
+        if "consolidated_metadata" in data and data["consolidated_metadata"] is not None:
             consolidated_metadata = ConsolidatedMetadata.from_dict(data["consolidated_metadata"])
         else:
             consolidated_metadata = None