Challenge 3: A Silent Blank Field in a 300-Letter Merge — Solution Walkthrough

What recipient 157's letter looks like:

The merge runs successfully for all 300 recipients, including row
157 — no error, no warning dialog, nothing flags that anything is
wrong. Recipient 157's printed letter reads exactly like every other
letter's template text, except wherever the «Amount» field was
inserted, that spot is simply blank — e.g. "you owe , due 8/15/2026"
with nothing filled in where a dollar figure should be. The letter
still prints, still gets sent, and looks otherwise completely normal
at a glance.

The habit that would have caught this before printing:

This chapter's own recommendation to spot-check SEVERAL merged
documents, not just the template and the first preview row, before
running the final print or send step. Using Preview Results and
clicking through a handful of different rows — ideally including some
scattered throughout the 300 records, not just the first few — would
have surfaced row 157's blank Amount value as an obviously wrong-
looking preview before a single page was ever printed. Alternatively,
reviewing the Excel source data itself for blank cells in required
columns (e.g. selecting the Amount column and checking its COUNT
against COUNTA per Excel Fundamentals Chapter 4's own distinction)
before ever starting the merge would have caught the missing value
even earlier.

WHY THIS WORKS AS AN ANSWER
------------------------------
This is a direct, concrete instance of this chapter's own warning:
Mail Merge doesn't error on a blank source cell, it just quietly
produces a blank result for that one recipient — identical in spirit
to Excel's own AVERAGE silently excluding a blank cell rather than
treating it as zero, or an approximate-match lookup silently
returning the wrong row. The fix in every one of these cases is the
same discipline: verify a sample of the actual output, don't just
trust that "it ran without an error" means "it ran correctly."