Object reference not set to an instance of an object - asp.net

Question

I keep getting the following error and I don't know how to fix it. Any help would be great please
Exception Details:NullReferenceException was unhandled by users code: Object reference not set to an instance of an object.
protected void LbUpload_Click(object sender, EventArgs e)
{
ERROR: if(FileUpload.PostedFile.FileName == string.Empty)
{
LabelMsg.Visible = true;
return;
}
else
{
string[] FileExt = FileUpload.FileName.Split('.');
string FileEx = FileExt[FileExt.Length - 1];
if (FileEx.ToLower() == "csv")
{
FileUpload.SaveAs(Server.MapPath("CSVLoad//" + FileUpload.FileName));
}
else
{
LabelMsg.Visible = true;
return;
}
}
CSVReader reader = new CSVReader(FileUpload.PostedFile.InputStream);
string[] headers = reader.GetCSVLine();
DataTable dt = new DataTable();
foreach (string strHeader in headers)
dt.Columns.Add(strHeader);
string[] data;
while ((data = reader.GetCSVLine()) != null)
dt.Rows.Add(data);
GridView1.DataSource = dt;
GridView1.DataBind();
if (FileUpload.HasFile)
try
{
FileUpload.SaveAs(Server.MapPath("confirm//") +
FileUpload.FileName);
LabelGrid.Text = "File name: " +
FileUpload.PostedFile.FileName + "<br>" +
FileUpload.PostedFile.ContentLength + " kb<br>" +
"Content type: " +
FileUpload.PostedFile.ContentType + "<br><b>Uploaded Successfully";
}
catch (Exception ex)
{
LabelGrid.Text = "ERROR: " + ex.Message.ToString();
}
else
{
LabelGrid.Text = "You have not specified a file.";
}
File.Delete(Server.MapPath("confirm//" + FileUpload.FileName));
}

Answer 1

You are checking if the FileName is string.Empty, it sounds like you want to detect when the user clicked the button without selecting a file.
If that happens, the actual PostedFile property will be null (remember, the user didn't posted a file), you should use the FileUpload.HasFile property for that purpose:
protected void LbUpload_Click(object sender, EventArgs e)
{
if(FileUpload.HasFile)
{
LabelMsg.Visible = true;
return;
}
// ...
}
But I would recommend you also to add a RequiredFieldValidator.
More on validation:
Validating ASP.NET Server Controls
ASP.NET Validation in Depth

Answer 2

Are you sure that FileUpload and FileUpload.PostedFile is not null?

Answer 3

Either FileUpload or its PostedFile property must be null.