> We find that if we use the substitution for that column, and its value is
> NULL, then the substitution is ignored.

I believe that this problem was fixed on 2001-09-19, although I do not
recall getting definite positive confirmation from the customer (but it has
been a while). The fix is of course included in 1.8e, but I do not think
this is always the best solution:

>  Dear &SALUTATION; &FIRST_NAME; &LAST_NAME;,

If SALUTATION is NULL (or the empty string), you will have two spaces
between "Dear" and the first name. This may not be a big deal in this
particular case, but in some cases it will be a problem. This can be avoided
using a conditional block:

.bb '&SALUTATION' = ''
Dear &FIRST_NAME; &LAST_NAME;,
.else
Dear &SALUTATION; &FIRST_NAME; &LAST_NAME;,
.eb

The mail-merge system makes no difference between NULL and the empty
string. Lower levels of LISTSERV can tell the difference, but once in the
mail-merge system it is the same thing. This is why you cannot compare
&SALUTATION with NULL.

Note that conditional blocks have a performance impact. Something like the
above is not a big deal, but if it occurs 20 times in the job it starts to become
another story. Running two jobs is always going to be more efficient.

  Eric