The problem of data loss after vuex refresh

vue project, after refreshing, the data in store is lost. I use localstorage to store it. When I take it out, I find that the page will report an error. I don"t know why.
Code:

methods: {
    ...mapMutations([
      "SET_USER",
    ]),
    Login(){
      Login(this.credentials.email,this.credentials.password)
      .then(res => {
        console.log(res.data,"")
        var data = res.data;
        if(data.error == ""){
          this.SET_USER(data.data);
          console.log(data.data);
          this.$router.go(-1);
        }
      })
    }
}

actions:

login(context, user) {
    context.commit(SET_USER, user);
},
getUser(context, user) {
    var data = {
        id: getStore("user_id"),//localStorage
        username: getStore("user_name"),
        session_id: getStore("session_id"),
    }
    context.commit(GET_USER, data)
}

mutations:

[SET_USER](state, user) {
    state.user = user;
    setStore("user_id", user.id);
    setStore("user_name", user.username);
    setStore("session_id", user.session_id);
},

[GET_USER](state, user) {
    state.user = user;
}

header component:

    <template v-if="user">
      <router-link to="/login" :exact="true"></router-link>
      <router-link to="/signin" :exact="true"></router-link>
    </template>
    <template v-else>
      <b-nav-item-dropdown :right="!isRTL" class="demo-navbar-user">
        <template slot="button-content">
          <span class="d-inline-flex flex-lg-row-reverse align-items-center align-middle">
            <span class="px-1 mr-lg-2 ml-2 ml-lg-0">{{ user.username }}</span>
          </span>
        </template>
        <b-dd-item><i class="ion ion-ios-person text-lightest"></i>  </b-dd-item>
        <b-dd-divider />
        <b-dd-item><i class="ion ion-ios-log-out text-danger"></i>  </b-dd-item>
      </b-nav-item-dropdown>
    </template>
    
    
    script:
    mounted(){
        this.getUser()
      },
      methods: {
        ...mapActions([
          "getUser"
        ]),
        toggleSidenav () {
          this.layoutHelpers.toggleCollapsed()
        },
    
        getLayoutNavbarBg () {
          return this.layoutNavbarBg
        }
      },
      computed: {
        ...mapState([
          "user"
        ])
      },

getStore and setStore:

/**
     * localStorage
     */
    export const setStore = (name, content) => {
        if (!name) return;
        if (typeof content !== "string") {
            content = JSON.stringify(content);
        }
        window.localStorage.setItem(name, content);
    }
    
    /**
     * localStorage
     */
    export const getStore = name => {
        if (!name) return;
        return window.localStorage.getItem(name);
    }
    
    /**
     * localStorage
     */
    export const removeStore = name => {
        if (!name) return;
        window.localStorage.removeItem(name);
    }

in this way, the page will throw an exception

vue-devtoolsstate