public Mapping GetMapping(string worksheetName, string colName)
        {
            Dictionary <string, Mapping> mappingDict = GetExtColNameToMappingDict(worksheetName);

            if (!mappingDict.TryGetValue(colName, out Mapping mapping))
            {
                MappingNotFoundException.SetMessageItems(worksheetName, colName);
            }

            return(mapping);
        }