Which of the following statements is correct ?

A A contract is voidable because it was caused by a mistake as to any law in force in India.

B A mistake as to law not in force in India has the same effect as a mistake of fact.

C A contract is voidable merely because it was caused by one of the parties to it being under a mistake as to a matter of fact.

D Where both the parties to an agreement are under a mistake as to a matter of fact essential to the agreement, the agreement is not void