Unexpected runtime error

The runtime has encountered an unexpected error.

Error source

Page Name:/sessionsbytrack.xsp
Control Id: approveButton

Exception

Error while executing JavaScript computed expression
Script interpreter error, line=1, col=24: 'sessions.getDocument()' is null

JavaScript code

   1: sessions.getDocument().getItemValueString("Status") != "Approved" && hasRole("[Admin]")

Stack Trace