Forum:Harpies' Hunting Ground

If I have on the field, "Harpies' Hunting Ground", the efect ( "When "Harpie Lady" or "Harpie Lady Sisters" is Normal Summoned or Special Summoned, destroy 1 Spell or Trap Card on the field" ) and my oponent doesn't have any spell or trap cards in his side of the field, but I have, I must destroy a spell or a trap card from side of the field?