The AI's cleaning draft "handled" missing values with one blanket drop — and three customers plus $114 of billed MRR vanished without a receipt. Replace the blanket drop with the three per-column decisions written in the comments, counting each as you go. No rows leave.
Expected output:
rows in 5, rows out 5
plan: filled 1 with 'unknown'
mrr: filled 1 with 0.0
region: kept 1 null(s)
july mrr: $212.00
The break is on lines 18, 19, 20, 21 — but read the whole snippet first.