Sec. 8. If the defendant in a case:
(1) is charged with unlawfully taking or detaining personal property or having done damage to personal property; and
(2) defends the charge in the defendant's pleading by asserting that the defendant is the executor, administrator, guardian, or heir, and, as such, has taken or detained the property or has done the acts charged;
a person is not competent to testify who would not be competent if the defendant were the complainant. However, when the person complaining cannot testify, the defendant shall also be excluded.