code: protected void duplicateCheck(int index, Integer previousIndex,
  			String column) {
  		if (previousIndex != null) {
  			throw new GeoPackageException("More than one " + column
  					+ " column was found for table '" + tableName + "'. Index "
  					+ previousIndex + " and " + index);
  
  		}
  	}
docs: Check for duplicate column names
  
  @param index
  index
  @param previousIndex
  previous index
  @param column
  column