What are the emails of employees with null commission, salary between 7000 and 12000, and who work in department 50?
return employees ;return commission of #1 ;return #1 where #2 is null ;return salary of #3 ;return #3 where #4 is higher than 7000 ;return #5 where #4 is lower than 12000 ;return #6 who  work in  department 50
['select', 'project', 'comparative', 'project', 'comparative', 'comparative', 'filter']