Refactor code slightly to avoid assert + fix D400 ruff check for fina…

…l period

dandiapi/api/management/commands/calculate_sha256.py

@@ -10,18 +10,16 @@
 @click.option('--blob-id', 'blob_id', help='Blob ID')
 @click.option('--asset-id', 'asset_id', help='Asset ID')
 def calculate_sha256(asset_id: str | None = None, blob_id: str | None = None):
-    """Trigger computation of sha256 for a blob
+    """Trigger computation of sha256 for a blob.
 
     Either blob-id or asset-id should be provided.
     """
     if not asset_id and not blob_id:
         raise ValueError('Provide either asset_id or blob_id')
 
-    if asset_id and blob_id:
-        raise ValueError('Provide only asset_id or blob_id, not both')
-
-    if not blob_id:
-        assert asset_id
+    if asset_id:
+        if blob_id:
+            raise ValueError('Provide only asset_id or blob_id, not both')
         asset = Asset.objects.get(asset_id=asset_id)
         blob_id = asset.blob_id