old_contents: # Copyright 2018 Graeme Gellatly
  # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
  
  from dateutil.relativedelta import relativedelta
  from odoo import api, fields, models
  
  
  class StatementCommon(models.AbstractModel):
  
      _name = 'statement.common.wizard'
      _description = 'Statement Reports Common Wizard'
  
      name = fields.Char()
      company_id = fields.Many2one(
          comodel_name='res.company',
          default=lambda self: self.env.user.company_id,
          string='Company'
      )
      date_end = fields.Date(required=True, default=fields.Date.context_today)
      show_aging_buckets = fields.Boolean(default=True)
      number_partner_ids = fields.Integer(
          default=lambda self: len(self._context['active_ids'])
      )
      filter_partners_non_due = fields.Boolean(
          string='Don\'t show partners with no due entries', default=True)
      filter_negative_balances = fields.Boolean(
          "Exclude Negative Balances", default=True
      )
  
      aging_type = fields.Selection(
          [("days", "Age by Days"), ("months", "Age by Months")],
          string="Aging Method",
          default="days",
          required=True,
      )
  
      account_type = fields.Selection(
          [('receivable', 'Receivable'),
           ('payable', 'Payable')], string='Account type', default='receivable')
  
      @api.onchange('aging_type')
      def onchange_aging_type(self):
          if self.aging_type == 'months':
              self.date_end = (
                  fields.Date.context_today(self).replace(day=1) -
                  relativedelta(days=1)
              )
          else:
              self.date_end = fields.Date.context_today(self)
  
      @api.multi
      def button_export_pdf(self):
          self.ensure_one()
          return self._export()
  
      def _prepare_statement(self):
          self.ensure_one()
          return {
              'date_end': self.date_end,
              'company_id': self.company_id.id,
              'partner_ids': self._context['active_ids'],
              'show_aging_buckets': self.show_aging_buckets,
              'filter_non_due_partners': self.filter_partners_non_due,
              'account_type': self.account_type,
              'aging_type': self.aging_type,
              'filter_negative_balances': self.filter_negative_balances,
          }
  
      def _export(self):
          raise NotImplementedError
  
new_contents: # Copyright 2018 Graeme Gellatly
  # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
  
  from dateutil.relativedelta import relativedelta
  from odoo import api, fields, models
  
  
  class StatementCommon(models.AbstractModel):
  
      _name = 'statement.common.wizard'
      _description = 'Statement Reports Common Wizard'
  
      name = fields.Char()
      company_id = fields.Many2one(
          comodel_name='res.company',
          default=lambda self: self.env.user.company_id,
          string='Company',
          required=True,
      )
      date_end = fields.Date(required=True, default=fields.Date.context_today)
      show_aging_buckets = fields.Boolean(default=True)
      number_partner_ids = fields.Integer(
          default=lambda self: len(self._context['active_ids'])
      )
      filter_partners_non_due = fields.Boolean(
          string="Don't show partners with no due entries", default=True)
      filter_negative_balances = fields.Boolean(
          "Exclude Negative Balances", default=True
      )
  
      aging_type = fields.Selection(
          [("days", "Age by Days"), ("months", "Age by Months")],
          string="Aging Method",
          default="days",
          required=True,
      )
  
      account_type = fields.Selection(
          [('receivable', 'Receivable'),
           ('payable', 'Payable')], string='Account type', default='receivable')
  
      @api.onchange('aging_type')
      def onchange_aging_type(self):
          if self.aging_type == 'months':
              self.date_end = (
                  fields.Date.context_today(self).replace(day=1) -
                  relativedelta(days=1)
              )
          else:
              self.date_end = fields.Date.context_today(self)
  
      @api.multi
      def button_export_pdf(self):
          self.ensure_one()
          return self._export()
  
      def _prepare_statement(self):
          self.ensure_one()
          return {
              'date_end': self.date_end,
              'company_id': self.company_id.id,
              'partner_ids': self._context['active_ids'],
              'show_aging_buckets': self.show_aging_buckets,
              'filter_non_due_partners': self.filter_partners_non_due,
              'account_type': self.account_type,
              'aging_type': self.aging_type,
              'filter_negative_balances': self.filter_negative_balances,
          }
  
      def _export(self):
          raise NotImplementedError
  
subject: Make company_id a required field in statement wizard