Changes to GET /public/get_book_summary_by_currency

the response property result/items/ask_price became nullable for the status 200

the response property result/items/bid_price became nullable for the status 200

the response property result/items/high became nullable for the status 200

the response property result/items/last became nullable for the status 200

the response property result/items/low became nullable for the status 200

the response property result/items/mid_price became nullable for the status 200

the response property result/items/price_change became nullable for the status 200

the response property result/items/open_interest became optional for the status 200