input: Write a function named validate_mail_list to verify if a list of email addresses is valid. The function should iterate through the list, validate each email using a regular expression, and return True if all emails are valid, otherwise return False. The regular expression used should validate emails with the structure "username@domain.extension". If the mail_list is empty, the function should return True.
  
  assert validate_mail_list(["example.user@gmail.com", "bad@example"]) == False
  assert validate_mail_list(["user.name@example.org", "another.user@domain.co"]) == True
  assert validate_mail_list(["user@sub.domain.com", "invalid.email@"]) == False
  assert validate_mail_list(["valid.email@domain.net", "another.valid@subdomain.co.uk"]) == True
  assert validate_mail_list([]) == True
output: import re
  
  def validate_mail_list(mail_list):
      if not mail_list:
          return True
      pattern = r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$'
      for email in mail_list:
          if not re.match(pattern, email):
              return False
      return True