Why am I getting an undefined method '<=' for in my ROR app

Question I have a custom divide and conquer array sorter that I would like to use. This all works well until I try to use it on an array in my controller I get this message.. NoMethodError (undefined method `<=' for #): Any help would be greatly appreciated thank you!

here is my Entry model with the mergesort method I am calling in my controller.

def self.mergesort(container)
  return container if (container.size <= 1)
  mid   = container.size / 2
  left  = container[0...mid]
  right = container[mid...container.size]
  merge(mergesort(left), mergesort(right))
end

def self.merge(left, right)
  sorted = []
  until left.empty? or right.empty?
    (left.first <= right.first) ? sorted << left.shift : sorted << right.shift
  end
  sorted + left + right
end

end end

Here is my Entry controller where I am trying to call it.

  def pending_sort 
    @ent_sort = Entry.where("section = ? and approve_disapprove = ?", @mgr_section, '3')


    @ent = Entry.mergesort(@ent_sort)

  end