Redis how to replace master which has no replica

I have a redis cluster with 3 master nodes: A, B, C. when node B lost，how can i add a new node D which should take over all slots of B (Note: we can discard all data in node B).

I try to send "forget B"(port:7001) to A(port:7000) & C(port 7002), then add new node D(port 7003), but it failed:

Comment From: itamarhaber

Hello @ustcr7 Keep in mind that this issue tracker should be used for reporting bugs or proposing improvements to the Redis server. Kindly close this issue. Questions should be directed to the community:

• the mailing list
• the redis tag at StackOverflow
• the irc channel #redis on freenode
• /r/redis subreddit