Related Clues:

• Null and __ (not valid)
• Null and __
• Empty math class
• Render inoperative
• "Null" companion
• ''___ where prohibited''
• "__ where prohibited22
• '___ where prohibited'
• Not valid; empty
• Worthless classical poet promoting his verse
• ___ where prohibited
• Not cashable
• Cancel, as a check
• Mathematical collection with nothing in it
• Useless little film receiving Oscar