Department a Required Field?

Hello,

Is the department field a required field for submitting an expense report? We have combination edit rules set up to require a department for specific accounts, which prevents these accounts to be submitted without a department. For the departments that do not fall under this rule I tried submitting an expense without a department and the blank field is bringing up an error that it is not a valid department. I don't get an error message stating it is a required field just that the department is not valid. Is it possible to submit an expense report without populating the