A DevOps team monitors a batch-processing Lambda function that only runs a few times per hour. They created a CloudWatch alarm on a custom 'ProcessingErrors' metric that the function publishes only when an error occurs. During periods when the function runs successfully, no data points are emitted for the metric. The team reports that the alarm frequently transitions to the INSUFFICIENT_DATA state and occasionally sends false alerts. They want the alarm to trigger only when actual errors are reported and to remain stable (not fire) during periods with no data. Which configuration change should they make?