Fixed.

The vmgrd daemon was incorrectly trying to read a NULL value into
a bind variable without an indicator.  There were two possible
solutions, prviode an indicator or use the SQL NVL() function.
The NVL() function was the simplest solution and this is what I
have implemented.

Please note that setting the tag of a tape to an empty string
causes the a NULL value to be created within the vmgr database.
If such a tag exists with a NULL value then it will be reported by
vmgrgettag as having a value of "none".  This is different from
the tag not existing at all, in which case vmgrgettag will display
the traditional error message of "No such file or directory".
Here are some examples:

[lxc2dev4] ~ > vmgrsettag -V V42005 --tag ''
[lxc2dev4] ~ > vmgrgettag -V V42005
none
[lxc2dev4] ~ > vmgrdeltag -V V42005
[lxc2dev4] ~ > vmgrgettag -V V42005
V42005: No such file or directory
[lxc2dev4] ~ >