undefined method `adjust_count_on_hand' for nil:NilClass

[Lordnibbler]

Since Spree 2.1.1, product.stock_items.first.adjust_count_on_hand(10) throws the error undefined methodadjust_count_on_hand' for nil:NilClass`.

Changing to product.master.stock_items.first.adjust_count_on_hand(10) fixes it.

@radar said: In product.rb, has_many :stock_items, through: :variants, rather than has_many :stock_items, through: :variants_including_master.

[radar]

Thanks for finding this @Lordnibbler.

The cause of this bug was that the stock_items association defined on the Product model was only fetching stock items for variants of that product that weren't the master variant. If the master variant is the only variant of this product, then no stock items at all were being returned.

I have submitted a fix for it to my 2-0-stable, 2-1-stable and master branches.