I am running odoo 11 community version and i am using the hotel management module. I am making a reservation and thereafter when I send a reservation email odoo displays below error. I got no clue, I could appreciate anyone's help coz am really new to odoo

Failed to render template <Template memory:7f08b0de65f8> using values {'format_date': <function MailTemplate.render_template.<locals>.<lambda> at 0x7f08c4bb90d0>, 'format_tz': <function MailTemplate.render_template.<locals>.<lambda> at 0x7f08c4bb9d08>, 'format_amount': <function MailTemplate.render_template.<locals>.<lambda> at 0x7f08c493ea60>, 'user': res.users(7,), 'ctx': {'lang': 'en_US', 'tz': False, 'uid': 7, 'params': {'action': 359}, 'active_model': 'hotel.reservation', 'active_id': 540, 'active_ids': [540], 'default_model': 'hotel.reservation', 'default_res_id': 540, 'default_use_template': True, 'default_template_id': 12, 'default_composition_mode': 'comment', 'force_send': True, 'mark_so_as_sent': True, 'search_disable_custom_filters': True, 'tpl_partners_only': True, 'safe': False}, 'object': hotel.reservation(540,)}