title: trying to combine multiple table for report in odoo, but it give me a blank error
body: <p>I am new around here, and I need some help<br><br>
  so, I am trying to make a report in odoo with <a href="https://apps.odoo.com/apps/modules/13.0/report_csv/" rel="nofollow noreferrer">Base report CSV</a>, in the table, I have 2 relational field, and I don't know how to combine those table, I tried combining the function from the module Base report CSV like below, but it give an error, a blank error which only make me confused, anyone got any idea how I could do this?</p>
  <pre><code>from odoo import models
  import csv
  
  class csvreport(models.AbstractModel):
      _name = 'report.hr_timesheet.report'
      _inherit = 'report.report_csv.abstract'
      def generate_csv_report(self, writer, data, partners):
          writer.writeheader()
          for obj in partners:
              employee = self.env.cr.execute(&quot;&quot;&quot;select hr_employee.name where hr_employee.id = %s;&quot;&quot;&quot;, (obj.employee_id))
              task = self.env.cr.execute(&quot;&quot;&quot;select project_task.name where project_task.id = %s;&quot;&quot;&quot;, (obj.project_id))
              writer.writerow({
                  'name': obj.name,
                  'date': obj.date,
                  'unit_amount': obj.unit_amount,
                  'responsible': employee.fetchall(),
                  'task': task.fetchall(),
              })
  
      def csv_report_options(self):
          res = super().csv_report_options()
          res['fieldnames'].append('name')
          res['fieldnames'].append('date')
          res['fieldnames'].append('unit_amount')
          res['fieldnames'].append('responsible')
          res['fieldnames'].append('task')
          res['delimiter'] = ';'
          res['quoting'] = csv.QUOTE_ALL
          return res
  </code></pre>
  <p>The Error : <br>
  <a href="https://drive.google.com/file/d/1Gz-4h9vXLYLg9iBtlWdx7RfjzTsmmwI7/view?usp=sharing" rel="nofollow noreferrer">Since i can't post picture, i'll just post a gdrive link</a></p>