title: Typescript React empty function as defaultProps
body: <p>I have a Stateless Functional Component with an optional function parameter as property (onClick), I tried to define an empty function as default property to be able to do safely in my component :</p>
  
  <pre><code> &lt;span onClick={props.onClick} /&gt;
  </code></pre>
  
  <p>But I have the following error : 'Expression expected.'</p>
  
  <pre><code>interface IProps {
    size?: sizeType;
    onClick?: (e:any) =&gt; void;
  }
  const Foo: React.SFC = (props: IProps) =&gt; {
    // ...
  };
  const defaultProps: IProps = {
     size: 'default',
     onClick: () =&gt; void &lt;-- Expression expected.
  };
  Foo = defaultProps;
  </code></pre>
  
  <p>How can I should do this?</p>