"auth.models.User is not saved, cant make cache key" error

bug
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When asking a question without registration following error occured:

ValueError at /questions/ask/

auth.models.User is not saved, cant make cache key

Request Method:     POST
Request URL:    [host:port]/questions/ask/
Django Version:     1.8.19
Exception Type:     ValueError
Exception Value:    

auth.models.User is not saved, cant make cache key

Exception Location:     /usr/local/lib/python2.7/site-packages/askbot-0.10.2-py2.7.egg/askbot/models/user_profile.py in get_profile_cache_key, line 15
Python Executable:  /usr/local/bin/python
Python Version:     2.7.15
Python Path:    

['/site',
 '/usr/local/lib/python27.zip',
 '/usr/local/lib/python2.7',
 '/usr/local/lib/python2.7/plat-linux2',
 '/usr/local/lib/python2.7/lib-tk',
 '/usr/local/lib/python2.7/lib-old',
 '/usr/local/lib/python2.7/lib-dynload',
 '/usr/local/lib/python2.7/site-packages',
 '/usr/local/lib/python2.7/site-packages/askbot-0.10.2-py2.7.egg',
 '/',
 '/usr/local/lib/python2.7/site-packages/askbot-0.10.2-py2.7.egg/askbot/deps']

How to fix it? As a registered user asking a question was succesfull. I'm using Askbot version 0.10.2