invariant.js:42 Uncaught Error: React.Children.only expected to receive a single React element child 2017年10月22日 2190 × 1530 【React対応】invariant.js:42 Uncaught Error: React.Children.only expected to receive a single React element child invariant.js:42 Uncaught Error: React.Children.only expected to receive a single React element child 上記の場合文字列まで返しているためエラー