I am trying to do parallel ssh on servers. While doing this, i am getting "TypeError: 'NoneType' object is not iterable" this error. Kindly help.

My script is below

```
from pssh import ParallelSSHClient
from pssh.exceptions import AuthenticationException, UnknownHostException, ConnectionErrorException

def parallelsshjob():
        client = ParallelSSHClient(['10.84.226.72','10.84.226.74'], user = 'root', password = 'XXX')
        try:
                output = client.run_command('racadm getsvctag', sudo=True)
                print output
        except (AuthenticationException, UnknownHostException, ConnectionErrorException):
                pass
        #print output

if __name__ == '__main__':
        parallelsshjob()

```

And the Traceback is below

```
Traceback (most recent call last):
  File "parallelssh.py", line 17, in <module>
    parallelsshjob()
  File "parallelssh.py", line 10, in parallelsshjob
    output = client.run_command('racadm getsvctag', sudo=True)
  File "/Library/Python/2.7/site-packages/pssh/pssh_client.py", line 520, in run_command
    raise ex
TypeError: 'NoneType' object is not iterable

```

Help me with the solution and also suggest me to use ssh-agent in this same script. Thanks in advance.