Fix: return empty string from output callbacks

This prevents cliapp.runcmd from collecting all output into
a (potentially large) internal buffer, which only gets thrown away
when it returns.

1 files changed, 1 insertions, 1 deletions

diff --git a/worker_manager b/worker_manager
index 3fc3220..85cd2b2 100755
--- a/worker_manager
+++ b/worker_manager
@@ -357,7 +357,7 @@ class Runner:
         self._buffers[stream_name] += data.decode('UTF-8')
         if len(self._buffers[stream_name]) >= self._maxbuf:
             self.flush()
-        return None
+        return b''
 
     def flush(self):
         logging.debug('flushing: self._buffers=%r', self._buffers)