code: function describeUnusableRecord(unusableRecord, batch, context) {
    const b = batch || context.batch;
    const state = b && b.states.get(unusableRecord);
    return `Unusable record (${state && state.recDesc})`;
  }
docs: A `describeItem` implementation that accepts and describes the arguments passed to a `discardUnusableRecord` function.
  @param {UnusableRecord} unusableRecord - the unusable record to be discarded
  @param {Batch} batch - the batch being processed
  @param {StreamConsumerContext} context - the context to use
  @returns {string} a short description of the unusable record