Fix nullability in UserAvatar
Fix nullability in UserAvatar

leotsarev/joinrpg-net,leotsarev/joinrpg-net,joinrpg/joinrpg-net,joinrpg/joinrpg-net,leotsarev/joinrpg-net,joinrpg/joinrpg-net,joinrpg/joinrpg-net,leotsarev/joinrpg-net