I forgot to say about columngroup. Exception appear if all fields in group doesn’t exists in data.
For example:
admin_notes: ""
coupon.duration: 0
coupon.expires_at: "01/01/3000"
id: 1
order.created_at: "04/14/2016"
order.id: 5
order.state: "Cancelled"
order.total_price: 4
order_id: 5
product.id: 1
product.name: "example"
can be exported, but:
admin_notes: ""
id: 1
order.created_at: "04/14/2016"
order.id: 5
order.state: "Cancelled"
order.total_price: 4
order_id: 5
product.id: 1
product.name: "example"
not
