Prevent "uninitialized value" warnings in parameter logging

Use of uninitialized value $p[0] in join or string at
/usr/local/share/perl/5.10.1/OpenSRF/Application.pm line 130.

This is caused when the array of method params contains null/undef
values.  Prevent the warnings by replacing these values w/ empty
strings.

Signed-off-by: Bill Erickson <berick@esilibrary.com>
Signed-off-by: Dan Scott <dscott@laurentian.ca>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>