NullReferenceException for CheckBox on RowDataBound using C# in ASP.Net

Hello, I'm trying to set the value of a checkbox in a gridview based on another column, but I get the error 'System.NullReferenceException' occurred

This is my code: 

protected void gvChecks_RowDataBound(object sender, GridViewRowEventArgs e)
{
   try
   {
      if (e.Row.RowType == DataControlRowType.DataRow)
      {
          Label checkResult = e.Row.FindControl("lblCheckResult") as Label;                 
          if (checkResult.Text == "TRUE")
          {
              CheckBox cbTrue = (CheckBox)e.Row.FindControl("cbYes");
              cbTrue.Checked = true;
          }
       }
    }
    catch (Exception ex)
    {
        myMessageBox(ex.Message);
    }
}

I would appreciated any kind of help.

Thank you in advance.