title: Cannot read property 'map' of undefined (Next.js)
body: <p>I write my app on Next.js. I get data from API. When I click on page "About" (below) I have error: Cannot read property 'map' of undefined, but when I restart this page - it works.
  How I can avoid this mistake?</p>
  
  <pre><code>import React from 'react'
  import Header from './Header'
  import Link from 'next/link'
  import axios from 'axios';
  
  export default class extends React.Component {
    static async getInitialProps () {
      if(!process.browser) {
        const res = await axios.get('https://api.themoviedb.org/3/movie/popular?api_key=2cdce3bbe05c745f380ca0af5874a2d8&amp;language=en-US&amp;page=1')
        return {data: res.data}
      } else {
        return {data: JSON.parse(sessionStorage.getItem('bpl'))}
      }
    }
  
    componentDidMount () {
      if(!sessionStorage.getItem('bpl')) sessionStorage.setItem('bpl', JSON.stringify(this.props.data))
    }
    render () {
  
      return (
        &lt;div&gt;
          &lt;Header /&gt;
  
          &lt;div className="pure-g"&gt;
              &lt;div className="pure-u-1-3"&gt;&lt;/div&gt;
              &lt;div className="pure-u-1-3"&gt;
                &lt;h1&gt;TOP Movies 2017&lt;/h1&gt;
  
                &lt;table className="pure-table"&gt;
                  &lt;thead&gt;
                    &lt;tr&gt;
                      &lt;th&gt;Title&lt;/th&gt;
                      &lt;th&gt;Popularity&lt;/th&gt;
                      &lt;th&gt;Overview&lt;/th&gt;
                    &lt;/tr&gt;
                  &lt;/thead&gt;
                  &lt;tbody&gt;
                  {this.props.data.results.map((results, id) =&gt; {
  
                    return (
                        &lt;tr key={id} &gt;
                          &lt;td className="title"&gt;&lt;p className="title_sign"&gt;{results.title}&lt;/p&gt;&lt;/td&gt;
                          &lt;td&gt;{results.popularity}&lt;/td&gt;
                          &lt;td&gt;{results.overview}&lt;/td&gt;
                        &lt;/tr&gt;
                      );
                  })}
                  &lt;/tbody&gt;
                &lt;/table&gt;
              &lt;/div&gt;
              &lt;div className="pure-u-1-3"&gt;&lt;/div&gt;
          &lt;/div&gt;
          &lt;style jsx&gt;{`
          h1 {
              text-align: center;
              margin-top: 40px;
              color: grey;
          }
        .title {
          width: 180px;
        }
        .title_sign {
          font-weight: 600;
        }
        th {
          color: grey;
        }
      `}&lt;/style&gt;
        &lt;/div&gt;
      );
    }
  }
  </code></pre>