title: MyPy syntax error when used Optional in the typing
body: <p>I have some rather innocent code using <code>Optional</code> in their typing, to claim they can be <code>None</code>. But mypy keeps giving me errors</p>
  <p>Actual code</p>
  <pre><code>from typing import TypedDict, Optional
  
  class Error(TypedDict):
      code: str
      message: Optional[str]
      field: Optional[str]
  </code></pre>
  <p>The error output by running <code>mypy .</code> <code>types.py</code> is the file contains that class, 12 line is the one with <code>message:Optional[str]</code></p>
  <blockquote>
  <p>clients/types.py:12:14: error: syntax error in type comment</p>
  </blockquote>
  <p>my mypy version is 0.770, python version is 3.9.2</p>
  <p>How to resolve this?</p>