UserMappingManager#createUserBean is not passed a username like the signature and implementation seem to expect, but a key. This causes the "user" variable to be null for some users when they don't have matching usernames/keys in the following piece of code:

    public UserBean createUserBean(final String userName)
    {
        Assertions.notBlank("userName", userName);
        ApplicationUser user = userManager.getUserObject(userName);
        if (user == null)
        {
            return null;
        }
        else
        {
            return new UserBean(user.getName(), user.getEmailAddress(), user.getDisplayName());
        }
    }

 
UserManager#getUserObject expects a username as argument.

End result is that, for example, comments belonging to such users don't get copied over.