VIP Persistence issue

When i dont mention VIP persistence name and keep it blank I get the below error,

Exception calling "add_persistence_profile" with "2" argument(s): "Exception caught in LocalLB::urn:iControl:LocalLB/Vi rtualServer::add_persistence_profile() Exception: Common::OperationFailed primary_error_code : 16908342 (0x01020036) secondary_error_code : 0 error_string : 01020036:3: The requested persist profile () was not found." At C:\Program Files (x86)\F5 Networks\iControlSnapIn\CreateBulkVIP_Copy.ps1:77 char:65 + (Get-F5.iControl).LocalLBVirtualServer.Add_persistence_profile <<<< ((,$vipset.VIPName),(,$vippersistence)) + CategoryInfo : NotSpecified: (:) [], MethodInvocationException + FullyQualifiedErrorId : DotNetMethodException

Can someone help to resolve the below error and i need the vip persistence to be blank because i dont want to keep persistence for every VIP.