Mvat / ptax return for nil transactions

I am registered dealer under mvat since 2006.  During current FY 2011-12  there was no taxable sale/purchase  (only service charges) in my company.  I have not  submitted any qtrly or half yearly returns during this year.  Do I need to submit NIL return for this period ( CST & VAT) even though there are no transactions.  Will there be any penalty for not submitting half yearly returns ?

Similarly I am also registered under P.Tax but don't have any employees.  Do I need to submit NIL return for P.Tax also ?

Ravi Modi