Drupal 9 Deprecated Code Report

Problem/Motivation

drupal-check on version:
193d8040de11745164a362efe7901ec17d30b0e1

2/2 [▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓] 100%

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  Line   src/Plugin/Block/GoBack.php                                                   
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  253    \Drupal calls should be avoided in classes, use dependency injection instead  
  270    \Drupal calls should be avoided in classes, use dependency injection instead  
  311    Variable $urlb might not be defined.                                          
  366    Variable $urlb might not be defined.                                          
  379    \Drupal calls should be avoided in classes, use dependency injection instead  
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 [ERROR] Found 5 errors