I am trying to parse the uncompressed file 10302018.NASDAQ_ITCH50 (from ftp://emi.nasdaq.com/ITCH/10302018.NASDAQ_ITCH50.gz). There is a strange message type "J". The spec (https://www.nasdaqtrader.com/content/technicalsupport/specifications/dataproducts/NQTVITCHspecification.pdf) does not contain any format for "J" message type. Is this corrupt data?
4.2.7 Limit Up – Limit Down (LULD) Auction Collar
Indicates the auction collar thresholds within which a paused security can reopen following a LULD Trading Pause
Name Offset Length Value Notes Message Type 0 1 “J” LULD Auction Collar