Check for nil member_partitions in RoundRobinAssignmentStrategy to prevent raising of TypeError when the number of clients in group exceeds the number of partitions.
Check for nil member_partitions in RoundRobinAssignmentStrategy to prevent raising of TypeError when the number of clients in group exceeds the number of partitions.

zendesk/ruby-kafka,crashlytics/ruby-kafka,crashlytics/ruby-kafka,zendesk/ruby-kafka