Forum:Book Of Life question

Hi there anyone/everyone. Ih have a small question concerning the spell card book of life.

here is the effect

Special Summon 1 Zombie-Type monster from your Graveyard and remove from play 1 monster from your opponent's Graveyard.

now my question is, am I forced to remove from play one of my opponent monster? for an example, he dosent have any monster card in is graveyard , can I still use this card?

thank you for your help :P