Reducer output seems to go to /dev/null when input is empty

[gsakkis]

The following script should generate the same output regardless of the input but it doesn't when the input is empty, despite yielding the same 100 entries as evidenced by the stderr messages:

import sys
import dumbo
from dumbo.lib import identitymapper

def reducer(data):
    for _ in data:
        pass
    for i in xrange(100):
        yield "foo", i        
        print >> sys.stderr, "yielding" , i

if __name__ == '__main__':
    dumbo.run(identitymapper, reducer)