title: wrappedComponentRef is undefined - React Ant Design, Form Component
body: <p>I am using Ant design - Form and Modal components with React.</p>
  
  <p>Form wrapper component:</p>
  
  <pre><code>class InsertForm extends React.Component{
      render(){
          const formItemLayout = {
              labelCol: { span: 24 },
              wrapperCol: { span: 24},
          };
          const { getFieldDecorator } = this.props.form;
          return (
              &lt;div&gt;
                  &lt;Form.Item
                      {...formItemLayout}
                      label="Title"
                  &gt;
                      {getFieldDecorator('title', {
  
                      })(
                          &lt;Input placeholder="Title" /&gt;
                      )}
                   &lt;/Form.Item&gt;
  ......
              &lt;/div&gt;
          )
      }
  }
  const InsertFormWrapper = Form.create()(InsertForm);
  </code></pre>
  
  <p>I am calling this component in another component in the same file (that's why I am not exporting the form component) inside a <code>Modal</code> and I am using <code>wrappedComponentRef</code>:</p>
  
  <pre><code>export default class InsertCont extends React.Component{
      constructor(props){
          super(props);
          console.log(this.form) // Undefined
      }
      insert = () =&gt; {
              console.log(this.form); // Not undefined
          }
      render(){
          &lt;Modal
              ...{modalProps}
              onOk={this.insert}
          &gt;
              &lt;InsertFormWrapper
                  wrappedComponentRef={(form) =&gt; this.form = form}
              /&gt;
          &lt;/Modal&gt;
      }
  }
  </code></pre>
  
  <p>The problem is that in the constructor the ref <code>this.form</code> is undefined, but if the modal is open and OK button is clicked - <code>onOk={this.insert}</code>  the ref is not undefined.</p>