title: Actions may not have an undefined "type" property. Have you misspelled a constant?
body: <p>My demo does not run well. </p>
  
  <p><a href="https://github.com/jiexishede/react-redux-demo01" rel="noreferrer">https://github.com/jiexishede/react-redux-demo01</a></p>
  
  <p>The error is : </p>
  
  <p><a href="https://i.stack.imgur.com/21Hd8.png" rel="noreferrer"><img src="https://i.stack.imgur.com/21Hd8.png" alt="enter image description here"></a></p>
  
  <p>I don't know how to solve this error. 
  The error stops me more than two hours.
  I have to ask someone help me.</p>