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subscribe_unsubscribe's call to self.command_queue.get(0) can return undefined.

See original GitHub issue

node_redis Version: 2.7.1
Redis Version: 3.2.4
Platform: Node.js 6.10.2 on Heroku
Description: subscribe_unsubscribe’s call to self.command_queue.get(0) can return undefined. This will cause the command_obj.args check to throw.

I’m unsure why this happens on our server on occasion, and I have been unable to reliably reproduce this issue. The only thing I can think of that might be causing the problem, based on the comments in the subscribe_unsubscribe function about the optional callback, is that we omit the callback in our subscribe and unsubscribe calls, e.g., pubSubClient.subscribe([channel1, channel2, etc...]);.

Let me know if you need any more information or if there is anything I can do to help.

Example stack trace:

/app/node_modules/redis/index.js:747 
      if (command_obj.args.length === 1 || self.sub_commands_left === 1 || command_obj.args.length === 0 && (count === 0 || channel === null)) { 
              ^ 
  TypeError: Cannot read property 'args' of undefined 
      at subscribe_unsubscribe (/app/node_modules/redis/index.js:747:20) 
      at return_pub_sub (/app/node_modules/redis/index.js:796:9) 
      at RedisClient.return_reply (/app/node_modules/redis/index.js:828:9) 
      at JavascriptRedisParser.returnReply (/app/node_modules/redis/index.js:192:18) 
      at JavascriptRedisParser.execute (/app/node_modules/redis-parser/lib/parser.js:574:12) 
      at Socket.<anonymous> (/app/node_modules/redis/index.js:274:27) 
      at emitOne (events.js:96:13) 
      at Socket.emit (events.js:188:7) 
      at readableAddChunk (_stream_readable.js:176:18) 
      at Socket.Readable.push (_stream_readable.js:134:10)