Error with clock?

[h.lansel]

Hello,

I am using Debian Stretch with XFCE.  I was customizing my clock, and 
encountered a few errors.  I don't know what package in relation to this 
software cause this and I don't even know how to do bug report, so I am writing 
to you, instead to bug report e-mail address.

Basically, I right click on clock, then click on properties.  Then on Clock 
Option, then I do custom format.  But whenever I enter any one of those four 
options below, the entire clock display disappears.

%N     nanoseconds (000000000..999999999)
%U     week number of year, with Sunday as first day of week (00..53)
%q     quarter of year (1..4)
%W     week number of year, with Monday as first day of week (00..53)

I am having the same problem with Xubuntu 18.04.  Also, I did not have this 
problem when I was using Debian Jessie.

Just wanted to let you know.