line item included tax being sent as $0

[dholdren]

Solidus Version: 2.3

I'm getting the following error stating that the total_tax_amount has a bad value when creating a session:

(byebug) Klarna.client(:credit).create_session(order)
#<Klarna::Response:0x00007f91ce808a60 @http_response=#<Net::HTTPBadRequest 400 Bad Request readbody=true>, @code=400, @body={"error_code"=>"BAD_VALUE", "error_messages"=>["Bad value: order_lines[0].total_tax_amount"], "correlation_id"=>"4c73c59f-f741-44db-a69b-22298902fc41"}, @headers={"content-type"=>["application/json"], "date"=>["Fri, 01 Jun 2018 17:32:51 GMT"], "klarna-correlation-id"=>["4c73c59f-f741-44db-a69b-22298902fc41"], "render-time"=>["1"], "server"=>["openresty"], "strict-transport-security"=>["max-age=31536000; includeSubDomains"], "content-length"=>["164"], "connection"=>["Close"]}>

The serialized order's order_lines have $0 for the total_tax_amount

(byebug) order
{:purchase_country=>"GB", :purchase_currency=>"GBP", :locale=>"en-GB", :order_amount=>35000, :order_lines=>[{:reference=>"MATTRESSSINGLEUK", :name=>"The Mattress", :quantity=>1, :unit_price=>35000, :tax_rate=>2000, :total_amount=>35000, :total_tax_amount=>0, :image_url=>nil, :product_url=>nil, :discount_amount=>0}, {:type=>"shipping_fee", :reference=>"H63134638705", :name=>"Parcel", :quantity=>1, :unit_price=>0, :total_amount=>0, :total_tax_amount=>0, :tax_rate=>0}], :merchant_reference1=>"R613395713", :options=>{}, :merchant_urls=>{:confirmation=>"http://casper.com/uk/en/orders/R613395713?completed=true&locale=", :notification=>"http://casper.com/uk/uk/en/klarna/callbacks/notification"}}

But the order's line items have a value for included_tax_total:

(byebug) Spree::Order.last.line_items
#<ActiveRecord::Associations::CollectionProxy [#<Spree::LineItem id: 7124026, variant_id: 173, order_id: 4280614, quantity: 1, price: #<BigDecimal:7f91eb69c178,'0.35E3',9(18)>, created_at: "2018-05-31 20:32:15", updated_at: "2018-05-31 20:32:16", cost_price: nil, tax_category_id: 2, adjustment_total: #<BigDecimal:7f91eb6900f8,'0.0',9(18)>, additional_tax_total: #<BigDecimal:7f91eb6936b8,'0.0',9(18)>, promo_total: #<BigDecimal:7f91eb692c18,'0.0',9(18)>, included_tax_total: #<BigDecimal:7f91eb6929c0,'0.5833E2',18(27)>, promotional_credit_total: #<BigDecimal:7f91eb692678,'0.0',9(18)>, deleted_at: nil>]>

Pinning the gem to sha ef6fdc7 resolves the issue and looking at the comparison
ef6fdc78f00c...43a2afb you'll see there's been a change to the way total_tax_amount is calculated