docs: def cases(ctx, case_id, to_json):
      """Display cases in the database."""
  
      adapter = ctx.obj['adapter']
      cases = []
  
      if case_id:
          case_obj = adapter.case({'case_id':case_id})
          if not case_obj:
              LOG.info("Case {0} does not exist in database".format(case_id))
              return
          case_obj['_id'] = str(case_obj['_id'])
          cases.append(case_obj)
      else:
          cases = adapter.cases()
          if cases.count() == 0:
              LOG.info("No cases found in database")
              ctx.abort()
  
      if to_json:
          click.echo(json.dumps(cases))
          return
  
      click.echo("#case_id\tvcf_path")
  
      for case_obj in cases:
          click.echo("{0}\t{1}".format(case_obj.get('case_id'), case_obj.get('vcf_path')))