Undefined array key รบกวนพี่ๆช่วยตรวจสอบหน่อยครับว่า error เกิดจากส่วนไหน

List Menu 
		  <select name="lmName1" OnChange="window.location='?item='+this.value;">
		  <option value="">Please Select Item </option>
		  <?php
           $sql = " SELECT * FROM tb_perios ORDER BY id ASC ";
           $result = mysqli_query( $con, $sql );

           while( $row = mysqli_fetch_assoc( $result) ) {
            {
				if($_GET["item"] == $row["id"])
				{
					$sel = "selected";
				}
				else
				{
					$sel = "";
				}
			?>
			<option value="<?php echo $row["id"];?>" <?php echo $sel;?>><?php echo $row["id"];?></option>
			<?php
            }
        }
			?>
		  </select>
          <?php
		  if($_GET["item"] != "" )
		  {
			$sql = "SELECT * FROM tb_perios WHERE id = '".$_GET["item"]."' ";
            $result2 = mysqli_query( $con, $sql );
            $row2 = mysqli_fetch_assoc( $result2);
		  }

		  ?>
		<input name="txtName" type="text" value="<?php echo $row2["month"];?>">