input: Write a function named send_emails that takes a list of recipient emails as input and iterates over the list to send an automated email to each email address. Use the given information to compose and send the email using the smtplib library. If the emails are sent successfully, print 'Email sent successfully.' If the list is empty, print 'No emails to send.'
  
  assert send_emails(["email1@example.com", "email2@example.com"])==None, 'Email sent successfully.'
  assert send_emails([])==None, 'No emails to send.'
output: def send_emails(recipient_emails):
      if not recipient_emails:
          print('No emails to send.')
          return
      
      for email in recipient_emails:
          # Placeholder for actual email sending logic using smtplib
          # Example: send_email_using_smtplib(email)
          pass
      
      print('Email sent successfully.')