code: def check_missing_references(client):
      
      from renku.models.refs import LinkReference
  
      missing = [
          ref for ref in LinkReference.iter_items(client)
          if not ref.reference.exists()
      ]
  
      if not missing:
          return True
  
      click.secho(
          WARNING + 'There are missing references.'
          '\n  (use "git rm <name>" to clean them)\n\n\t' + '\n\t  '.join(
              click.style(str(ref.path), fg='yellow') + ' -> ' +
              click.style(str(ref.reference), fg='red') for ref in missing
          ) + '\n'
      )
      return False
docs: Find missing references.