Javascript document.getElementById("id").value returning null instead of empty string when the element is an empty text box

I have a text box element whose value I am trying to access using document.getElementById("id-name").value. I find that the call is returning a null instead of empty string. The data-type of the returned value is still string. Is null a string value?

<input type="text" value="" id="mytext"> is the textbox whose value I am trying to fetch using var mytextvalue = document.getElementById("mytext").value;