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

test/decentralised_book_index/sync/data_transformers/author_transformer_test.exs

@@ -29,5 +29,23 @@ defmodule DecentralisedBookIndex.Sync.DataTransformers.AuthorTransformerTest do
         description: "Something"
       } = author
     end
+
+    test "a json doesn't contains author information \"data\" attribute" do
+      json_body = %{
+        "attributes" => %{"description" => "Something", "name" => "Author"},
+        "id" => "889a323e-d104-4b5d-b276-dad5a9b1da9d",
+        "links" => %{},
+        "meta" => %{},
+        "relationships" => %{},
+        "type" => "author"
+      }
+
+      assert {:ok, author} = AuthorTransformer.from_json(json_body)
+      assert %{
+        id: "889a323e-d104-4b5d-b276-dad5a9b1da9d",
+        name: "Author",
+        description: "Something"
+      } = author
+    end
   end
 end