title: How to get the pull request number from predefined variable in azure build pipeline(CI)
body: <p>I need PR number on which my CI kickoff.I am using System.PullRequest.PullRequestNumber but it is showing empty string when my CI is running.</p>
  
  <p><a href="https://i.stack.imgur.com/EyDku.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/EyDku.png" alt="enter image description here"></a></p>
  
  <p>Write-Host "PR Number is:-" $env:System.PullRequest.PullRequestNumber</p>
  
  <p><strong>I am not running this CI through save and queue. Following the complete process of PR.</strong></p>