Improve enhancer sad path

app/models/book/enhancer.rb

@@ -5,11 +5,14 @@ def update_from_api
     api_data = OpenLibraryApi.get_book(book.isbn)
     return unless api_data
 
+    isbns = api_data["isbn_13"] || []
+
     attrs = {
-      isbn: api_data["isbn_13"].first,
+      isbn: isbns.first,
       pages: api_data["number_of_pages"],
       title: api_data["title"]
-    }
+    }.compact
+    return unless attrs.any?
 
     book.update!(attrs)
   end

spec/models/book/enhancer_spec.rb

@@ -25,6 +25,20 @@
       end
     end
 
+    context "with empty api data" do
+      let(:api_data) { {} }
+      let(:isbn) { "123456789" }
+
+      it "does nothing" do
+        expect(OpenLibraryApi).to receive(:get_book).and_return(api_data)
+        book.enhancer.update_from_api
+
+        expect(book.isbn).to eq "123456789"
+        expect(book.pages).to eq nil
+        expect(book.title).to eq nil
+      end
+    end
+
     context "with a book that has none for isbn" do
       let(:isbn) { "none" }