Sum returning null - sql

Question

I am having a problem with a Ruby SQL look up function: it always returns a null.
Here is the terminal output:
SELECT COUNT("point_store_items"."point_cost")
FROM "point_store_items"
INNER JOIN "point_store_items_point_store_orders"
ON "point_store_items"."id" = "point_store_items_point_store_orders"."point_store_item_id"
WHERE "point_store_items_point_store_orders"."point_store_order_id" IS NULL
The code causing this problem is:
def self.pointcost
self.count(:point_cost)
end
If this code is changed to say
def self.pointcost
40
end
it has no issues except the prices always listed is 40, not what should come from the database.
Relevant Model Code:
class PointStoreItem < ActiveRecord::Base
attr_accessible :product_id, :point_cost
has_and_belongs_to_many :orders, :class_name => "PointStoreOrder"
has_many :users, :through => :orders
belongs_to :product
def to_param
"#{id}-#{product.name.parameterize}"
end
def self.pointcost
self.count(:point_cost)
end
end
The model that calls for the pointcost
class PointStoreOrder < ActiveRecord::Base
include Workflow
attr_accessible :point_transaction_id, :user_id, :workflow_state , :shipping_provider, :tracking_number, :items
has_and_belongs_to_many :items, :class_name => "PointStoreItem"
belongs_to :user
belongs_to :point_transaction
accepts_nested_attributes_for :items
workflow do
state :cart do
event :purchase, :transitions_to => :purchased
event :cancel, :transitions_to => :cancelled
end
state :purchased do
event :ship, :transitions_to => :shipped
end
state :shipped
state :cancelled
end
def purchase
unless self.user.point_balance >= total
halt "Insufficient point balance"
else
self.point_transaction = user.point_transactions.new
self.point_transaction.point_count = total
self.point_transaction.save!
self.save!
end
end
def total
self.items.pointcost
end
def on_cancelled_entry(old_state, event, *args)
end
end