code: @Override
     public Integer getColumnIndex(String name) {
        if (null == header) {
           throw new IllegalStateException("The header row hasn't been read yet.");
        }
  
        createIndexLookup(header);
  
        return indexLookup.get(name);
     }
docs: Gets the column index that corresponds to a specific colum name.
  If the CSV file doesn't have a header row, this method will always return
  null.
  
  @param name the column name
  @return the column index, or null if the name doesn't exist