add bugsnag alert

app/models/spree/variant.rb

@@ -300,6 +300,7 @@ module Spree
     end
 
     def ensure_unit_value
+      Bugsnag.notify("Trying to set unit_value to NaN") if unit_value&.nan?
       return unless (product&.variant_unit == "items" && unit_value.nil?) || unit_value&.nan?
 
       self.unit_value = 1.0