title: Cannot read property 'state' of null
body: <p>I have an input and a button</p>
  
  <pre><code>&lt;input className="form-control" value={this.state.sentence} onChange={this.onChange}/&gt;
  &lt;button type="button" onClick={this.handleSentence}&gt;&lt;/button&gt;
  </code></pre>
  
  <p>I have binded both functions in constructor.</p>
  
  <pre><code>onChange(e) {this.setState({sentence: e.target.value});}
  
  handleSentence(e) {console.log('string --&gt;',this.state.sentence)}
  </code></pre>
  
  <p>on handleSentence function the <code>log</code> returns <code>Cannot read property 'state' of null</code>.</p>
  
  <p>but in <code>render(let{sentence}=this.state)</code> returns the correct value and also I see what I type in input</p>
  
  <p><strong><em>here is the constructor:</em></strong></p>
  
  <pre><code>class SentenceForm extends Component {
      constructor(props) {
          super(props)
          this.state = {
              sentence: '',
              splitedSentenceArray:[]
          }
          this.onChange = this.onChange.bind(this);
          this.onClick = this.handleSentence.bind(this);
      }
  </code></pre>