This is one of those cases where browsers are different from the spec. (BTW, the spec you are looking for is here https://url.spec.whatwg.org/)

It really depends on the browser. Here are a few test cases to consider. http://jsfiddle.net/8e525ne9/

Leading nulls used to work in common browsers. Most recent browsers don't support it. However, most do continue to support fun things like newlines and tabs in the middle of URL schemes.