code: def _get_element_attr_or_none(document, selector, attribute):
      
      element = document.cssselect(selector)
      if element:
          return element[0].get(attribute)
      return None
docs: Using a CSS selector, get the element and return the given attribute value, or None if no element.
  
      Args:
          document (HTMLElement) - HTMLElement document
          selector (str) - CSS selector
          attribute (str) - The attribute to get from the element