我的组件：

<div id="event-picker">
  <template v-for="event in $store.state.events">
    <a href="#" v-on:click.prevent="$store.dispatch('prepareEventForm', event)">{{ event.artist }}</a>
  </template>
</div>

我的商店（突变）：

prepareEventForm(state, event) {
  state.form.time = event.time
  state.form.date = event.date
  state.form.event = event.event
  state.form.artist = event.artist
  state.form.organizer = event.organizer
  state.form.location = event.location
  state.showForm = true
}

我得到的错误是Cannot read property 'time' of undefined
问题出在哪里？
编辑：
这是我的行动方法：

prepareEventForm({ commit }) {
  commit('prepareEventForm')
}