[Devel] do_assign: no value in right expression

[Juha Heinanen]

my proxy got a request that had no From URI userpart, i.e., from uri
looked like

From: sip:foo;tag=bar

i had an xlog statement in openser.cfg that assigns from uri userpart
($fU) to a pseudo variable.  as result, i get to syslog:

do_assign: no value in right expression

in these kind of situations, would it possible to assume that right
expression has value NULL and not to produce the syslog message?  it
would namely be too cumbersome to each time test if a thing is not
NULL before the assignment.

-- juha