isTrivialMackeyFunctor MChecks whether $M$ is trivial (meaning isomorphic to the zero Mackey functor).
The object isTrivialMackeyFunctor is a method function.
The source of this document is in /build/macaulay2-88fgJW/macaulay2-1.25.11+ds/M2/Macaulay2/packages/CpMackeyFunctors/Documentation/HomomorphismsDoc.m2:321:0.