Fix issue with cooperative assignor when rebalance_cb is a boolean

Author: milindl

lib/kafka-consumer.js

@@ -62,9 +62,17 @@ function KafkaConsumer(conf, topicConf) {
       // That's it
       try {
         if (err.code === -175 /*ERR__ASSIGN_PARTITIONS*/) {
-          self.assign(assignment);
+          if (self.rebalanceProtocol() === 'COOPERATIVE') {
+            self.incrementalAssign(assignment);
+          } else {
+            self.assign(assignment);
+          }
         } else if (err.code === -174 /*ERR__REVOKE_PARTITIONS*/) {
-          self.unassign();
+          if (self.rebalanceProtocol() === 'COOPERATIVE') {
+            self.incrementalUnassign(assignment);
+          } else {
+            self.unassign();
+          }
         }
       } catch (e) {
         // Ignore exceptions if we are not connected