Mass. Gen. Laws ch. 277, § 37: Negativing excuses, exceptions or provisos

Section 37. An excuse, exception or proviso not stated in the enacting clause of a statute creating a crime or stated only by reference to other provisions of the statute need not be negatived in the indictment unless necessary for a complete definition of the crime. If any statute shall prescribe a form of indictment in which an excuse, exception or proviso is not negatived, it shall be taken that it is not necessary to a complete definition of the crime that they should be negatived. If a statute creating a crime permits an act, therein declared to be criminal, to be performed without criminality under stated conditions, such conditions need not be negatived.