php error when submitting form on the same page

Question

my problem is that when i submitting form on the same page i am getting this error : Undefined index: myname on line 46 name is empty , i don't know what is exact problem , can any one resolve this issue ?

<form action="<?php echo $_SERVER['PHP_SELF'];?>" method="post">
    name : <input type="text" name="myname">
    <input type="submit">
</form>
<?php
if($_SERVER["REQUEST_METHOD"]=="POST")
{
    $name=$_POST['myname'];
    if(empty($name)){
        echo "name is empty";
    }
    else{
        echo  "name is $name";
    }
}
?>