make sequence field nullable and blankable
make sequence field nullable and blankable

BjornFJohansson/giraffe,addgene/giraffe,BjornFJohansson/giraffe,UndeadBlow/giraffe,BjornFJohansson/giraffe,addgene/giraffe,BjornFJohansson/giraffe,UndeadBlow/giraffe,addgene/giraffe,addgene/giraffe,BjornFJohansson/giraffe