dsl.WordCount doesn't print result on a local cluster

[manuzhang]

The following application is run on a local cluster and (is,1)(bingo!!,2)(a,1)(good,1)(This,1)(start,,1) is expected in gearpump-local-*.log

    val app = StreamApp("dsl", context)
    val data = "This is a good start, bingo!! bingo!!"
    app.source(data.lines.toList, 1, "source").
      // word => (word, count)
      flatMap(line => line.split("[\\s]+")).map((_, 1)).
      // (word, count1), (word, count2) => (word, count1 + count2)
      groupByKey().sum.map(print)