title: Error "Please enter a correct entity model." while Importing CSV in custom module in Magento 2
body: <p>I receive this error when i'm trying to import a list of <code>sellers</code> (custom module). I want to know what is the meaning of this error? and where should I start to fix the problem?
  <a href="https://i.stack.imgur.com/ovCQM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ovCQM.png" alt="X Please enter a correct entity model."></a></p>
  
  <p><strong>PS</strong>: Please let me know if you need more info.</p>