Sorting an array based on an attribute that may be nil in some elements

I have an array of objects

[<#a star=1  val=1>, <#a star=nil val=3> , <#a star=2  val=2>]

i need the array to be sorted by time, then by val

[ <#a star=2  val=2>, <#a star=1  val=1>, <#a star=nil val=3> ]

but using the sort_by throws an error because the time is nil.

I am using an ugly way to sort right now, but i am sure there is a nice way to go about it

starred=[]
@answers.each {|a| (starred << a) if a.starred }
@answers=@answers-starred
starred=starred.sort_by {|a| a.starred }.reverse
@answers=starred+@answers