ReactJS选择选项占位符未被提取

Question

我使用值映射填充select-options，循环遍历值映射并将它们添加到选项中。但是，作为占位符，我希望显示一些默认文本。但它没有被接受。不确定我做错了什么。

import React, {Component} from 'react';
class DropdownComponent extends React.Component {

handleChange(event) {
        this.setState({value: event.target.value});
    }

    render() {
        return (
            <select onChange={this.handleChange.bind(this)}>

                {
                    this.props.valueMap.map((i) => {
                        return <option key={i.code} placeholder={this.props.placeholder}
                                       value={i.code}>{i.code}</option>

                    })}
            </select>
        )
    }
}
DropdownComponent.defaultProps = {
    name: 'womensObstetrics.referralReason',
    htmlFieldtype: 'select',
    placeholder: 'Reason for referral',
    label: 'Reason for referral',
    valueMap: [
        {
            code: "Some code",
            label: "Please Select"
        },
        {
            code: "Maternity",
            label: "Maternity"
        },
        {
            code: "Other",
            label: "Other"
        }
    ]
}
export default DropdownComponent;

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