quarantine doesnt work "value should be of type unicode"

[suptimal]

Request Method: GET
https://mail.netzwerkplan.de/quarantine/listing/?sort_order=-date&reset_page=true
1.11.11
AssertionError
value should be of type unicode
/usr/local/lib/python2.7/dist-packages/modoboa_amavis/utils.py in fix_utf8_encoding, line 63
/usr/bin/python
2.7.6
['/usr/lib/python2.7', '/usr/lib/python2.7/plat-x86_64-linux-gnu', '/usr/lib/python2.7/lib-tk', '/usr/lib/python2.7/lib-old', '/usr/lib/python2.7/lib-dynload', '/usr/local/lib/python2.7/dist-packages', '/usr/lib/python2.7/dist-packages', '/usr/lib/pymodules/python2.7', '/var/www/mailadmin']
Fri, 23 Mar 2018 04:12:26 +0100

stacktrace: http://dpaste.com/1XVA3X4

SELECT DEFAULT_CHARACTER_SET_NAME
FROM INFORMATION_SCHEMA.SCHEMATA
WHERE SCHEMA_NAME = "amavis";
+----------------------------+
| DEFAULT_CHARACTER_SET_NAME |
+----------------------------+
| latin1 |
+----------------------------+