How to invoke getImageURI method on chart about react-google-charts HOT 9 CLOSED

<div id='extremeIssuesTrendChart' style={{"zIndex": 2}}>
      <Chart ref='googleChart' chartType = "ComboChart" data = {data} options = {options} graph_id = "ScatterChart"  width={"100%"} height={"400px"}  legend_toggle={true} />
    </div>

const chart = ReactDOM.findDOMNode(this.refs.googleChart);
const img = chart.getImageURI();
console.log('Image is ', img);

import React  from 'react';
import {render} from 'react-dom'
import {Chart} from 'react-google-charts'
class ExtremeIssuesTrendChart extends React.Component {

  componentDidMount = () => {
    console.log('Props in trend chart are', this.props);
    console.log('Chart  ', this.GoogleChart);
    const googleChart = this.GoogleChart;
    for (let prop in googleChart) {
      if (googleChart.hasOwnProperty(prop)){
        console.log('Prop is', prop, 'And value is ', googleChart[prop]);
      }
    }
    console.log('Chart data is ', this.GoogleChart['chart']);
    this.props.setChartUri(this.GoogleChart.chart.getImageURI())
  };

  render() {
    const options = {
      title : 'Extreme Issues trend',
      vAxis: {title: 'Amount'},
      hAxis: {title: 'Fix Version'},
      seriesType: 'bars'};
      const data = [];
    data.push(['FixVersion', 'Bug', 'Total', 'Other']);
    this.props.stories.map(fixVersionDetails => {
      const detailsArray = [];
      detailsArray.push(fixVersionDetails.fixVersion);
      detailsArray.push(fixVersionDetails.bug);
      detailsArray.push(fixVersionDetails.total);
      detailsArray.push(fixVersionDetails.other);
      data.push(detailsArray);
    });

    return (
    <div id='extremeIssuesTrendChart' style={{"zIndex": 2}}>
      <Chart ref={(ref) => this.GoogleChart = ref}
             chartType = "ComboChart"
             data = {data}
             options = {options}
             graph_id = "ScatterChart"
             width={"100%"}
             height={"400px"}
             legend_toggle={true}
      />
    </div>
    );
  }
}

export default ExtremeIssuesTrendChart;

Chart   Chart {props: Object, context: Object, refs: Object, updater: Object, state: Object…}
Prop is props And value is  Object {chartType: "ComboChart", data: Array[9], options: Object, graph_id: "ScatterChart", width: "100%"…}
Prop is context And value is  Object {}
Prop is refs And value is  Object {}
Prop is updater And value is  Object {}
Prop is state And value is  Object {graphID: "ScatterChart"}
Prop is chart And value is  null
Prop is wrapper And value is  null
Prop is hidden_columns And value is  Object {}
Prop is dataTable And value is  []
Prop is _reactInternalInstance And value is  ReactCompositeComponentWrapper {_currentElement: Object, _rootNodeID: 0, _compositeType: 0, _instance: Chart, _hostParent: ReactDOMComponent…}
Chart data is  null
Uncaught TypeError: Cannot read property 'getImageURI' of null

<div id='extremeIssuesTrendChart' style={{"zIndex": 2}}>
      <Chart ref={(ref) => this.GoogleChart = ref}
             chartType = "ComboChart"
             data = {data}
             options = {options}
             graph_id = "ScatterChart"
             width={"100%"}
             height={"400px"}
             legend_toggle={true}
             chartEvents = {this.state.chart_events}
      />
    </div>

constructor() {
    super();
    this.state = {'chart_events': undefined};
  }