title: Right way of using react-hook-form with typescript and material-ui for showing error message
body: <p>I am using react-hook-form with typescript and material-ui. I wanted to pass error message as a <code>helperText</code> to <code>TextField</code>. I have tried to do so using 
  <code>helperText={errors.email?.message}</code>
  but typescript complains about this assignment. </p>
  
  <pre><code>Property 'email' does not exist on type 'NestDataObject&lt;FormData&gt;'.ts(2339)
  </code></pre>
  
  <p>I don't want to disable this rule from my .eslintrc file, because it may ignore other similar issues in my application, which may be desired at some places.
  What is the right way of assigning error message of react-hook-form as a helperText to material-ui components? </p>
  
  <p>codesandbox link 
  <a href="https://codesandbox.io/s/material-ui-react-form-hook-yi669" rel="nofollow noreferrer">https://codesandbox.io/s/material-ui-react-form-hook-yi669</a></p>