Stage - Getting server error on adding additional rule from edit rule button available on standard/new hire rule

Log in to stage as partner
Select any company, we have tried it on UI Test - City of Irvine
go to Benadmin -> ACA - Measurement and Stability
edit exiting rule
click on Edit rule button
Click on Select a rule from top drop down
Provide details for all fields
click on Save button

Actual result - Getting server error
expected result - should save without error

ERROR LOG
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ErrorID : 0
ErrorSource : ControllerAppTier.GetData->WORKTERRAControllerAppTier.GetData->GenericEligibilityRule.GetData->GenericEligibilityRule.GetRuleMappingDetailsForViewDependency
ErrorMessage: Conversion from type 'DBNull' to type 'String' is not valid.
StackTrace: at WORKTERRA.Shared.WORKTERRAControllerAppTier.GetData(WORKTERRAControllerWebTierEntity objWORKTERRAControllerWebTierEntity)
at WORKTERRA.ControllerAppTier.GetData(Int32 intProjectsId, String strInput)
TargetSite: System.String GetData(WORKTERRA.Shared.WORKTERRAControllerWebTierEntity)