Update AuthorTransformer to check if the "data" attibute is available.

lib/decentralised_book_index/sync/data_transformers/author_transformer.ex

@@ -3,11 +3,20 @@ defmodule DecentralisedBookIndex.Sync.DataTransformers.AuthorTransformer do
   alias DecentralisedBookIndex.Metadata.Author
 
   def from_json(json_body) do
-    author = %{
-      id: get_in(json_body, ["data", "id"]),
-      name: get_in(json_body, ["data", "attributes", "name"]),
-      description: get_in(json_body, ["data", "attributes", "description"]),
-    }
+    author =
+      if Map.has_key?(json_body, "data") do
+        %{
+          id: get_in(json_body, ["data", "id"]),
+          name: get_in(json_body, ["data", "attributes", "name"]),
+          description: get_in(json_body, ["data", "attributes", "description"]),
+        }
+      else
+        %{
+          id: get_in(json_body, ["id"]),
+          name: get_in(json_body, ["attributes", "name"]),
+          description: get_in(json_body, ["attributes", "description"]),
+        }
+      end
 
     {:ok, author}
   end