title: React: TypeError: existingChildren.set is not a function
body: <p>I am trying to call setState in the success function of axios and I am getting below error:</p>
  
  <pre><code>Uncaught TypeError: existingChildren.set is not a function
      at mapRemainingChildren (react-dom.development.js:6824)
      at reconcileChildrenArray (react-dom.development.js:7320)
      at reconcileChildFibers (react-dom.development.js:7672)
      at reconcileChildrenAtExpirationTime (react-dom.development.js:7788)
      at reconcileChildren (react-dom.development.js:7771)
      at updateHostComponent (react-dom.development.js:8024)
      at beginWork (react-dom.development.js:8257)
      at performUnitOfWork (react-dom.development.js:10244)
      at workLoop (react-dom.development.js:10308)
      at HTMLUnknownElement.callCallback (react-dom.development.js:540)
      at Object.invokeGuardedCallbackDev (react-dom.development.js:579)
      at invokeGuardedCallback (react-dom.development.js:436)
      at renderRoot (react-dom.development.js:10386)
      at performWorkOnRoot (react-dom.development.js:11000)
      at performWork (react-dom.development.js:10952)
      at requestWork (react-dom.development.js:10861)
      at scheduleWorkImpl (react-dom.development.js:10744)
      at scheduleWork (react-dom.development.js:10706)
      at Object.enqueueSetState (react-dom.development.js:6204)
      at App../node_modules/react/cjs/react.development.js.Component.setState 
   (react.development.js:226)
      at App.js:86
      at &lt;anonymous&gt;
  </code></pre>
  
  <p>This is the code from where the error is getting generated:</p>
  
  <pre><code>componentDidMount() {
     axios
       .get('/api/fetchMapData')
       .then(
         function(response) {
           this.setState({ mapData: response.data });
         }.bind(this)
       )
       .catch(function(error) {
         console.log(error);
       });
   }
  </code></pre>
  
  <p>I assume it has something to do with the way I am rendering the component which causes the issue.</p>
  
  <pre><code>render() {
      return (
        &lt;div className="app"&gt;
          &lt;Header /&gt;
          &lt;BreadCrumb
            data={this.state.breadCrumb}
            setCountryView={this.setCountryView.bind(this)}
          /&gt;
          &lt;Switch&gt;
            &lt;Route
              exact
              path="/"
              component={() =&gt;
                &lt;Home
                  setMapView={this.setMapView.bind(this)}
                  mapData={this.state.mapData}
                /&gt;}
            /&gt;
            &lt;Route path="/country/:country" component={Country} /&gt;
          &lt;/Switch&gt;
        &lt;/div&gt;
      );
  </code></pre>
  
  <p>Any suggestion on this is highly appreciated.</p>