title: Material Ui Datepicker is giving error: expected a string
body: <p>I am trying to implement a Datepicker in my React Project using the Material UI's DatePicker. I initially tried to do what <a href="https://material-ui.com/components/pickers/" rel="nofollow noreferrer">this</a> site said. After that didn't work, I tried a simpler approach and tried what <a href="https://material-ui-pickers.dev/demo/datepicker" rel="nofollow noreferrer">this</a> site said. Both those approaches give this error:</p>
  <pre><code>Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. You likely forgot to export your component from the file it's defined in, or you might have mixed up default and named imports.
  
  Check the render method of `AddScreen`.
  </code></pre>
  <p>My CodeSandbox link: <a href="https://codesandbox.io/s/testing-karmapact-app-bghgp?file=/App.js" rel="nofollow noreferrer">https://codesandbox.io/s/testing-karmapact-app-bghgp?file=/App.js</a> (Datepicker is implemented in /Screens/AddScreen.js)</p>