Difference between Convert.ToString() VS .ToString() method

Convert.ToString  handles null and not throws ObjectReferenceNullException. ToString does not handles the null value and throws the null exception error message.

Example:--

    public String FullName = null;

    protected void Page_Load(object sender, EventArgs e)

    {

        try

        {

            Response.Write("<b>.ToString</b><br>");

            Response.Write("FullName :" + FullName.ToString());

        }

        catch (Exception ex)

        {

            Response.Write(ex.Message);

        }

        Response.Write("<br><br>");

        try

        {

            Response.Write("<b>Convert.ToString</b><br>");

            Response.Write("FullName :" + Convert.ToString(FullName));

        }

        catch (Exception ex)

        {

            Response.Write(ex.Message);

        }

    }