Element UI select多选验证

<el-form-item label="业务领域" prop="businessArr">
                      <el-select v-model="businessArr"
                                   multiple
                                   filterable
                                   collapse-tags
                                   placeholder="请选择" style="width:93%">
                            <el-option v-for="item in businessList"
                                       :key="item.CRMTagID"
                                       :label="item.Name"
                                       :value="item.CRMTagID">
                            </el-option>
                        </el-select>
                    </el-form-item>



 rules: {
                //业务领域
                businessArr: [
                    {
                        validator: function (rule, value, callback) {
                            if (vm.businessArr.length === 0) {
                                callback(new Error('请选择业务领域'));
                            } else {
                                callback();
                            }
                        },
                    },
                ],
               
            },