質問編集履歴
1
エラーコード追記
    
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| 14 14 | 
             
            ```
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| 15 15 | 
             
            Cannot read property 'toLowerCase' of undefined
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| 16 16 | 
             
            TypeError: Cannot read property 'toLowerCase' of undefined
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| 17 | 
            +
                at ReactDOMServerRenderer.renderDOM (/usr/src/app/node_modules/react-dom/cjs/react-dom-server.node.development.js:2776:28)
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| 18 | 
            +
                at ReactDOMServerRenderer.render (/usr/src/app/node_modules/react-dom/cjs/react-dom-server.node.development.js:2755:23)
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| 19 | 
            +
                at ReactDOMServerRenderer.read (/usr/src/app/node_modules/react-dom/cjs/react-dom-server.node.development.js:2722:19)
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| 20 | 
            +
                at renderToString (/usr/src/app/node_modules/react-dom/cjs/react-dom-server.node.development.js:2980:25)
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| 21 | 
            +
                at renderPage (/usr/src/app/node_modules/next/dist/server/render.js:174:26)
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| 22 | 
            +
                at Function.getInitialProps (/usr/src/app/node_modules/next/dist/server/document.js:83:25)
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| 23 | 
            +
                at Function._callee$ (/usr/src/app/pages/_document.js:6:25)
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| 24 | 
            +
                at tryCatch (/usr/src/app/node_modules/babel-runtime/node_modules/regenerator-runtime/runtime.js:65:40)
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| 25 | 
            +
                at Generator.invoke [as _invoke] (/usr/src/app/node_modules/babel-runtime/node_modules/regenerator-runtime/runtime.js:299:22)
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| 26 | 
            +
                at Generator.prototype.(anonymous function) [as next] (/usr/src/app/node_modules/babel-runtime/node_modules/regenerator-runtime/runtime.js:117:21)
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| 17 27 | 
             
            ```
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| 18 28 | 
             
            refを使う方法も試してみたのですが、いまいち理解できずこちらもエラーが起きてしまいました。
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| 19 29 |  |