Randal embezzled $6000 of his employer's money and then disappeared. The employer's accountant called at Randal's residence and found out that his wife had a $3500 term deposit. When the accountant threatened to have her husband arrested and imprisoned if she did not agree, she assigned the term deposit to the employer to help to defray the loss from the embezzlement.

If the wife wants to sue later for return of the term deposit, what would be her ground for avoiding the assignment? Discuss the legal principle.