Timecards are getting auto approved when i have left the payroll time type field blank

Summary:

Timecards are getting auto approved when i have left the payroll time type field blank. We have made payroll time type field non required due to some requirements. We have tried all the conditions as below one by one and tried manager hierarchy .Still the transaction is getting auto approved.
(ApprovalTimeRecordGroup.attributeChar10 != "Regular Element CH")
(ApprovalTimeRecordGroup.attributeChar10 == null)
(ApprovalTimeRecordGroup.payrollTimeType == null)
Can you guide if i am missing something?

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