code: public void setColumnSpec(int columnIndex, ColumnSpec columnSpec) {
          checkNotNull(columnSpec, "The column spec must not be null.");
          colSpecs.set(columnIndex - 1, columnSpec);
      }
docs: Sets the ColumnSpec at the specified column index.
  
  @param columnIndex the index of the column to be changed
  @param columnSpec the ColumnSpec to be set
  @throws NullPointerException if {@code columnSpec} is {@code null}
  @throws IndexOutOfBoundsException if the column index is out of range