title: Create warning message if cell left blank in google sheets
body: <p>Could someone please assist me with this?</p>
  
  <p>I would like a warning message (data validation) if B3 and C3 equal <code>"Absent"</code> or <code>"Late"</code> and B4 and C4 are empty?</p>
  
  <p><img src="https://i.stack.imgur.com/YlVKp.png" alt="Screenshot of spreadsheet"></p>