duplicity crashed with wrong parameters

[Szőke Károly]

Error message is:
 [abrt] duplicity: duplicity:1552:<module>:UnicodeEncodeError: 'ascii' codec can't encode character u'\u0151' in position 23: ordinal not in range(128)
System: Fedora 20
Kernel: 3.14.4-200.fc20.x86_64
Python 2.7.5
duplicity-0.6.24-2.fc20
duply version 1.6.0
  Using installed duplicity version 0.6.24, python 2.7.5, gpg 1.4.16 (Home: ~/.gnupg), awk 'GNU Awk 4.1.0, API: 1.0'.

It is called by duply frontend, the command was:
duply laptop purge jan 21 --force
I don't know, how should I use purge parameter, and I gave it: jan 21 (21 of january)

The details of error:
--- Start running command PURGE at 21:37:32.789 ---
Traceback (most recent call last):
  File "/usr/bin/duplicity", line 1552, in <module>
    if "Forced assertion for testing" in str(e):
UnicodeEncodeError: 'ascii' codec can't encode character u'\u0151' in position 23: ordinal not in range(128)
21:37:33.678 Task 'PURGE' failed with exit code '1'.
--- Finished state FAILED 'code 1' at 21:37:33.678 - Runtime 00:00:00.889 ---

Version-Release number of selected component:
duplicity-0.6.24-2.fc20

Additional info:
reporter: libreport-2.2.2
cmdline: /usr/bin/python /usr/bin/duplicity remove-older-than jan --name duply_laptop --encrypt-key C87E0D35 --sign-key C87E0D35 --verbosity 4 --use-agent --force file:///home/karcsi/backup/
executable: /usr/bin/duplicity
kernel: 3.14.4-200.fc20.x86_64
runlevel: N 5
type: Python
uid: 1000

Truncated backtrace:
#1 <module> in /usr/bin/duplicity:1552