Some programs allow you to specify which real and null (that is, randomized) runs you want.
For example, for the real run and 10 null runs,
The so-called null index of the real run is -1. All null indexes with value of 0 or greater refer to actual nulls.
For example, for just the real run
For 30 nulls
The real run, and nulls 2 through 5 and 15 through 20