input: Write a function to clean a string of HTML tags using regular expressions. The function should remove all HTML tags from the input string and return the cleaned text. If the input string is empty, the function should return an empty string.
  assert clean_html_tags("<p>This is a <b>test</b> string</p>")=="This is a test string"
  assert clean_html_tags("No tags here")=="No tags here"
  assert clean_html_tags("")==""
  assert clean_html_tags("<div><p><b>Multiple tags</b></p></div>")=="Multiple tags"
  assert clean_html_tags("<a href='example.com'>Link</a>")=="Link"
output: import re
  
  def clean_html_tags(text):
      if not text:
          return ""
      return re.sub(r'<[^>]+>', '', text)