Perl issue after upgrade from 4.0.19 to 4.2.12

Hello,

I was running RT 4.0.19 on Ubuntu 14.04 AMD64 with apache, mysql, 
external auth ldap and fastcgi.

Being unable to upgrade to 16.04 due to an Ubuntu issue, i set up a new 
virtual machine with Ubuntu 16.04 AMD64 and installed request-tracker 
from the ubuntu package, then imported and upgraded manually my database.

I'm now running Apache 2.4.18, MySQL 5.7.15 and RT 4.2.12.

Now, everything seems to work fine, except i got a white page with an 
error message from time to time (refreshing the page usually fixes the 
issue).

Here's my apache log :

[1680] [Tue Oct 11 15:43:23 2016] [warning]: Negative repeat count does 
nothing at /usr/share/perl5/Text/Quoted.pm line 244. 
(/usr/share/perl5/Text/Quoted.pm:244)
[1680] [Tue Oct 11 15:43:23 2016] [warning]: Negative repeat count does 
nothing at /usr/share/perl5/Text/Quoted.pm line 244. 
(/usr/share/perl5/Text/Quoted.pm:244)
[1680] [Tue Oct 11 15:43:23 2016] [warning]: Negative repeat count does 
nothing at /usr/share/perl5/Text/Quoted.pm line 244. 
(/usr/share/perl5/Text/Quoted.pm:244)
[1579] [Tue Oct 11 15:43:29 2016] [critical]: HasRights called with no 
valid object (/usr/share/request-tracker4/lib/RT/Principal.pm:381)
[1579] [Tue Oct 11 15:43:29 2016] [error]: Can't call method "id" on 
unblessed reference at /usr/share/request-tracker4/lib/RT/Principal.pm 
line 384.

Stack:
   [/usr/share/request-tracker4/lib/RT/Principal.pm:384]
   [/usr/share/request-tracker4/lib/RT/Interface/Web.pm:661]
   [/usr/share/request-tracker4/lib/RT/Interface/Web.pm:369]
   [/usr/share/request-tracker4/html/autohandler:53] 
(/usr/share/request-tracker4/lib/RT/Interface/Web/Handler.pm:209)

Any idea ?

Thanks,

-- 
Guillaume

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