1. The rate estimator should not estimate any rate when there are no records in the batch, as there is no data to estimate the rate. In the current state, it estimates and set the rate to zero. That is incorrect.
2. The rate estimator should not never set the rate to zero under any circumstances. Otherwise the system will stop receiving data, and stop generating useful estimates (see reason 1). So the fix is to define a parameters that sets a lower bound on the estimated rate, so that the system always receives some data.