Reactjs react：validateDOMNesting：#text cannot appear as a child of

你能给我解释一下为什么要显示警告Warning: validateDOMNesting(...): #text cannot appear as a child of <tr>. See Router > RouterContext > CarWashPage > AllCarWashTable > tr > #text.吗？我在标签tr里没有看到任何文字

Code that renders table

export default class AllCarWashTable extends React.Component{

constructor(props) {
    super(props);
    this.generateHeaders = this.generateHeaders.bind(this);
    this.generateRows = this.generateRows.bind(this);
};

static propTypes = {
    cols : React.PropTypes.array.isRequired,
    rows : React.PropTypes.array.isRequired
}

generateHeaders() {
    let cols = this.props.cols;  // [{key, label}]
    return cols.map(function(colData) {
        return <th key={colData.key}> {colData.label} </th>;
    });
}

generateRows() {
    let cols = this.props.cols,  // [{key, label}]
        data = this.props.rows;
    if (this.props.rows.length > 0) {
        return data.map(function(item) {
            var cells = cols.map(function(colData) {
                return <td key={colData.key}> {item[colData.key]} </td>;
            });
            return <tr key={item.id}> {cells} </tr>;
        });
    }
}

render(){
    let headers = this.generateHeaders();
    let rows = this.generateRows();

    return (
         <table className="table table-hove">
             <thead>
                <tr>
                    {headers}
                </tr>
             </thead>
             <tbody>
                    {rows}
             </tbody>

         </table>
    )
}
}

最后，my table has the following structure

问题出在哪里？