### What problem does this feature solve? in function normalizeNamespace make payload to string is so pain; can we add the typeOf(val) to judege this type? my English is poor, please forgive me ### What does the proposed API look like? I want to use mapMutations set payload mutations,like Vuex.mapMutations({ increame: { type: 'increame', addNum: 10 } }) <!-- generated by vue-issues. DO NOT REMOVE -->