No error handling for null google books data

[jose-marquez89]

When a google books api call returns with no books, the 'items' key will be missing from the json response. This causes a KeyError in recommender.py. Error handling here is necessary:

 def db_insert(self, isbn=None):
        api = GBWrapper()
        if isbn is not None:
            google_books_response = api.search(isbn)
        else:
            google_books_response = api.search(self.googleId)

        # INSERTS GB_QUERY INTO DATABASE
        logging.debug("GETTING API DATA...")
        # add error handling for the line below:
        api_data = get_value(google_books_response['items'][0])
        if isbn is not None:
            gid = api_data[0]
            details = retrieve_details(google_books_response)
        else:
            gid = None
            details = None
        # execute_queries(api_data, self.conn, self.cursor)
        execute_queries(api_data, self.conn)
        return gid, details