从硒中读取excel数据的问题c＃

Question

这是我的excel助手类

join

这是我的主要课程，我在其中调用excel帮助函数

using ExcelDataReader;
using System;
using System.Collections.Generic;
using System.Data;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EAAutoFramework.Helpers
{
public class ExcelHelpers
{
    private static List<Datacollection> _dataCol = new 
    List<Datacollection();

    // <summary>
    // Storing all the excel values in to the in-memory collections
    // </summary>
    // <param name="fileName"></param>
    public static void PopulateInCollection(string fileName)
    {
        DataTable table = ExcelToDataTable(fileName);

        //Iterate through the rows and columns of the Table
        for (int row = 1; row <= table.Rows.Count; row++)
        {
            for (int col = 0; col < table.Columns.Count; col++)
            {
                Datacollection dtTable = new Datacollection()
                {
                    rowNumber = row,
                    colName = table.Columns[col].ColumnName,
                    colValue = table.Rows[row - 1][col].ToString()
                };
                //Add all the details for each row
                _dataCol.Add(dtTable);
            }
        }
    }

    private static DataTable ExcelToDataTable(string fileName)
    {
        using (var stream = File.Open(fileName, FileMode.Open, 
        FileAccess.Read))
        {
            using (var reader = ExcelReaderFactory.CreateReader(stream))
            {
                var result = reader.AsDataSet(new 
                ExcelDataSetConfiguration()
                {
                    ConfigureDataTable = (data) => new 
                    ExcelDataTableConfiguration()
                    {
                        UseHeaderRow = true,
                    }
                });
                DataTableCollection table = result.Tables;
                //Store it in DataTable
                DataTable resultTable = table["Sheet1"];
                //return
                return resultTable;
            }
          }
        }

     public static string ReadData(int rowNumber, string columnName)
    {
        try
        {
            //Retriving Data using LINQ to reduce much of iterations
            string data = (from colData in _dataCol
                           where colData.colName == columnName && 
                           colData.rowNumber == rowNumber
                           select colData.colValue).SingleOrDefault();


            return data.ToString();
        }
        catch (Exception e)
        {
            return null;
        }
     }

   }

 public class Datacollection
  {
    public int rowNumber { get; set; }
    public string colName { get; set; }
    public string colValue { get; set; }
   }
 }

但是我无法从excel中读取数据，它会抛出空引用错误Message: Test method EAEmployeeTest.UnitTest1.TestMethod1 threw exception: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.ArgumentNullException: text cannot be null Parameter name: text

任何人都可以帮我解决这个问题。提前致谢