input: Write a function to remove HTML tags from a given string. The function should return the cleaned string without any HTML tags. 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("<div><p>Hello</p></div>") == "Hello"
  assert clean_html_tags("<a href='example.com'>Link</a>") == "Link"
  assert clean_html_tags("") == ""
  assert clean_html_tags("<p>Just text</p>") == "Just text"
output: import re
  
  def clean_html_tags(s):
      if not s:
          return ""
      return re.sub(r'<.*?>', '', s)