title: How to fix 'source.lift is not a function' error in angular?
body: <p>I'm using a custom version of the <a href="https://stackblitz.com/angular/vmvalpqyrde?file=src%2Fapp%2Fheroes%2Fheroes.service.ts" rel="noreferrer">angular project</a> <code>source.lift is not a function</code> when the <strong>http get</strong> call is made. The error is in <code>core.js</code> file.</p>
  
  <p>How to fix this issue?</p>
  
  <p><a href="https://i.stack.imgur.com/uBI0q.png" rel="noreferrer"><img src="https://i.stack.imgur.com/uBI0q.png" alt="enter image description here"></a></p>