验证v-combobox验证不起作用

<v-combobox v-model="value" :rules="[
  v => !!v || '该字段为必填项',
  v => (v && v.length <= 10) || '最多只能输入10个字符'
]"></v-combobox>

<v-combobox v-model="value" :rules="rules" :error-messages="errorMessages"></v-combobox>

data() {
  return {
    value: '',
    rules: [
      v => !!v || '该字段为必填项',
      v => (v && v.length <= 10) || '最多只能输入10个字符'
    ],
    errorMessages: []
  };
}

<v-combobox ref="myCombobox" v-model="value" :rules="rules" :error-messages="errorMessages"></v-combobox>
<button @click="validateCombobox">验证</button>

methods: {
  validateCombobox() {
    this.$refs.myCombobox.validate();
  }
}