Modular is defined in CR 702.43. It has two parts: a creature with modular enters the battlefield with a certain number of +1/+1 counters on it, and when it dies, you may move those counters to a target artifact creature.
The triggered ability reads 'when this creature dies, you may put a +1/+1 counter on target artifact creature for each +1/+1 counter on this creature.' If the modular creature has zero +1/+1 counters at the time it dies — whether because they were all removed beforehand or because it entered with zero — the ability triggers but there are simply zero counters to distribute. Moving zero counters has no visible effect.
The trigger still goes on the stack (you can still target an artifact creature), but resolving it with zero counters accomplishes nothing. CR 702.43b confirms the effect is based on the number of counters on the creature at the moment it dies.
Example: You control a Arcbound Worker (Modular 1) that had both its +1/+1 counters removed by Vampire Hexmage. When it later dies, the modular ability triggers. You may target another artifact creature, but since the Worker has zero +1/+1 counters, zero counters are moved — the target artifact creature is unchanged.
Note that the number of counters is checked as the creature leaves the battlefield (the last-known information principle, CR 702.43b and CR 608.2g), so only the counters actually on it at that moment matter.
Unofficial fan resource — not affiliated with or endorsed by Wizards of the Coast. Answers are AI-generated estimates grounded in the Comprehensive Rules and are not a substitute for an official judge. Verify anything match-critical.