The packages at flutter/packages need to be migrated to null safety.

I'll update this issue with a list once I've done an audit to see which ones actually make sense to migrate at this point (not all are used as traditional packages), but for anyone interested in contributing before I've done that, multicast_dns and palette_generator are almost certainly on that list.

• pointer_interceptor
• palette_generator
• pigeon (pending [pigeon] 0.2.0 Made null-safe generation the default, updated documentation  packages#315)
• multicast_dns (migrate mDNS to null safety packages#297)