System.Data.SqlTypes.SqlNullValueException: Data is Null.This method or property cannot be called on Null values.

Hello,
I am getting below error :
 

System.Data.SqlTypes.SqlNullValueException: Data is Null. This method or property cannot be called on Null values.
   at System.Data.SqlClient.SqlBuffer.get_Int64()
   at System.Data.SqlClient.SqlDataReader.GetInt64(Int32 i)

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This comes on line row[7] where it is assigning Date value. This is assigning to DataRow in Datatable , Please help.Thanks I checked there are data available in reader there is nothing like NULL for data. There is data present.

                    while (dr.Read() == true)
                    {
                        
                        if (Uid!= dr.GetInt32(0))
                        {

                            row = table.NewRow();
                            rectificationId = dr.GetInt32(0);
                            row[0] = dr.GetInt32(14);
                            row[1] = IdTest; 
                            row[2] = dr.GetString(1); 
                            row[3] = dr.GetInt32(2); 
                            row[4] = dr.IsDBNull(4) ? 0 : dr.GetInt32(4);                           
                            row[5] = dr.IsDBNull(6) ? string.Empty : dr.GetString(6); 
                            row[6] = dr.GetString(11); 
                         [b]   row[7] = new DateTime(dr.GetInt64(12)); [/b]
                            row[8] = new DateTime(dr.GetInt64(8)); 
                            row[9] = new DateTime(dr.GetInt64(9)); 
                            row[10] = dr.GetString(7); 
                            row[11] = dr.GetInt32(5); 
                            row[12] = dr.GetString(10); 
                            if (dr.IsDBNull(15))
                                row[14] = DBNull.Value;
                            else
                                row[14] = new DateTime(dr.GetInt64(15)); 


                          

}

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