Struggling with Object Reference Null Exception ASP.NET

I am having issues with DataTable.

I am trying to create a simple cart but it's not passing all the information to the Cart page when I click Add Cart.

<asp:ImageButton ID="ImageButton1" runat="server" ImageUrl='<%# ResolveUrl(Eval("Image").ToString()) %>'/>
    </div>
    <div>
        <b>
            <asp:Label ID="IDLABEL" runat="server" Text='<%# Eval("jumperID") %>'></asp:Label><br />
            <asp:Label ID="NameLabel" runat="server" Text='<%# Eval("Name") %>'></asp:Label><br />
            <asp:Label ID="TypeLabel" runat="server" Text='<%# Eval("Type") %>'></asp:Label> <br />
        </b></div>
    <div style="clear: right;">
        Our Price: £<%# Eval("Price") %></div>
    <asp:TextBox ID="txtQty" runat="server" Text="1" CssClass="QtyTextBox"></asp:TextBox>
    <div class="cell1">
        <asp:Button ID="btnCart" runat="server" Text="Add to Cart" CommandArgument='<%# Eval("jumperID") %>' OnClick="btnCart_Click"/></div>

When I click the add button it should pass information: jumperid, jumpername, type, quantity and price

However I get the error, and it highlights string JumperName...

"Object Reference not set"

string jumperID = Convert.ToInt32((((Button)sender).CommandArgument)).ToString();
string JumperName = ((Label)listView.FindControl("NameLabel")).Text;
string Type = ((Label)listView.FindControl("TypeLabel")).Text;
string Qty = ((TextBox)listView.FindControl("txtQty")).Text;

if (Session["Cart"] != null)
{
    DataTable dt = (DataTable)Session["Cart"];
    dt.Rows.Add(jumperID);
    dt.Rows.Add(JumperName);
    dt.Rows.Add(Type);
    dt.Rows.Add(Qty);
    Session["Cart"] = dt;
    Response.Redirect("MyCart.aspx");
}
else {
    DataTable dt = new DataTable();
    dt.Columns.Add(("jumperID"),typeof(string));
    dt.Rows.Add(jumperID);
    dt.Rows.Add(JumperName);
    dt.Rows.Add(Type);
    dt.Rows.Add(Qty);
    Session["Cart"] = dt;
    Response.Redirect("MyCart.aspx");
}

Please help me I've been stuck on it for a week now