code: public DataSetBuilder remainingColumnsNull() {
      for (int i = 0; i < fillers.length; i++) {
        if (fillers[i] == null) {
          fillers[i] = NULL_FILLER;
          fillerCount++;
        }
      }
      return this;
    }
docs: Set the NULL value filler for all remaining columns.
  
  <p>
  A call to this method sets the {@link #nullValue} filler
  for all columns without an associated filler.
  </p>
  @return  The builder instance (for chained calls).
  @see #nullValue(String)
  @see #allColumnsNull()