<template>
  <div class="pagination">
    <el-row type="flex" justify="end" >
      <el-pagination
        background
        @size-change="handleSizeChange"
        @current-change="handleCurrentChange"
        :current-page="currentPage"
        :page-sizes="pageSizes"
        :page-size="pageSize"
        :pager-count="5"
        layout="sizes, prev, pager, next, jumper"
        :total="total">
      </el-pagination>
    </el-row>
  </div>
</template>

点击页数修改时，或者每页显示条数 都会报如下错误

vue.esm.js?efeb:591 [Vue warn]: Error in event handler for "size-change": "TypeError: Cannot read property 'toLowerCase' of undefined"

怎么修改这个错误？