title: SqlConnection giving object reference error
body: <p>I have to use connection string for my query, but I am getting an error </p>
  
  <blockquote>
    <p>object reference not set to an instance of an object.</p>
  </blockquote>
  
  <p>This is my code:</p>
  
  <pre><code>string strSql = "select first_name + ' ' + last_name name, email from user_mst where mkey in (" + Session["UserId"].ToString() + ")";
  
  DataTable table = new DataTable();
  
  using (SqlConnection conn = new SqlConnection(System.Configuration.ConfigurationManager.AppSettings["ConnectionString"].ToString()))
  {
      conn.Open();
  
      using (SqlDataAdapter dbdata = new SqlDataAdapter(strSql, conn))
      {
          dbdata.Fill(table);
      }
  
      conn.Close();
  }
  </code></pre>
  
  <p>I get error at</p>
  
  <pre><code>SqlConnection conn = new SqlConnection(System.Configuration.ConfigurationManager.AppSettings["ConnectionString"].ToString()))
  </code></pre>
  
  <p>but my connections seems to be exactly fine.</p>