Object reference does not point to an instance of an object, error. How to fix?

Question

C++ / C#

Hello! !Tell me PLEASE WHAT IS THE PROBLEM? Gives an error
System.NullReferenceException: "Object reference does not point to an instance of an object."
result was null.

using (OpenFileDialog ofd = new OpenFileDialog() { Filter = "Excel Files|*.xls;*.xlsx;*.xlsm" })
            {
                if (ofd.ShowDialog() == DialogResult.OK)
                {
 
 
                 
                    FileStream fs = File.Open(ofd.FileName, FileMode.Open, FileAccess.Read);
                    Excel.IExcelDataReader reader = Excel.ExcelReaderFactory.CreateBinaryReader(fs);
                    reader.IsFirstRowAsColumnNames = true;
                    result = reader.AsDataSet();
                    CLEAR.Items.Clear();
                    
                    foreach (DataTable dt in result.Tables)
                    {
                        dt.TableName = "tab";
                        CLEAR.Items.Add(dt.TableName);
 
                    }
                    // dataGridView1.DataSource = dt.DefaultView;
 
                    reader.Close();
 
 
 
                }
            }
 
        }

Here is this line And moreover, when the xls file is doing everything is fine, and when xlsx gives an error
foreach (DataTable dt in result.Tables)

Answer 1

Your library only works with the xls format, or other methods are used to work with the xlsx format. Read the documentation for your Excel library.