code: public static Span exact(Bytes row, Column col) {
      Objects.requireNonNull(row);
      Objects.requireNonNull(col);
      RowColumn start = new RowColumn(row, col);
      return new Span(start, true, start.following(), false);
    }
docs: Creates a Span that covers an exact row and {@link Column}. The {@link Column} passed to this
  method can be constructed without a qualifier or visibility to create a Span at the family or
  qualifier level.