input: Write a function to extract titles of all YouTube videos from a given URL. The function should use the requests library to fetch the content of the URL and the re library to extract the titles using regular expressions. If the URL is empty or invalid, the function should return an empty list.
  assert extract_youtube_video_titles("https://www.youtube.com/user/Thexvid/videos")==['title1', 'title2']
output: def extract_youtube_video_titles(url):
      if not url:
          return []
      import requests
      import re
      try:
          response = requests.get(url)
          response.raise_for_status()
      except:
          return []
      titles = re.findall(r'<title>(.*?)</title>', response.text)
      return titles