code: public Object get(String columnId) throws CmsIllegalArgumentException {
  
          if ((getMetadata().getColumnDefinition(columnId) == null)
              && (getMetadata().getItemDetailDefinition(columnId) == null)) {
              throw new CmsIllegalArgumentException(
                  Messages.get().container(Messages.ERR_LIST_INVALID_COLUMN_1, columnId));
          }
          return m_values.get(columnId);
      }
docs: Returns the value of the column for this item.<p>
  
  @param columnId the column id
  
  @return the content, may be <code>null</code>
  
  @throws CmsIllegalArgumentException if the given <code>columnId</code> is invalid