Fix assert fail on empty document

This closes #20

parser/src/parser.rs

@@ -124,8 +124,7 @@ impl<T: Iterator<Item=char>> Parser<T> {
 
     fn parse<R: EventReceiver>(&mut self, recv: &mut R)
         -> ParseResult {
-        if self.scanner.stream_ended()
-            || self.state == State::End {
+        if self.state == State::End {
             return Ok(Event::StreamEnd);
         }
         let ev = try!(self.state_machine());

parser/src/yaml.rs

@@ -331,6 +331,14 @@ c: [1, 2]
         assert!(doc["d"][0].is_badvalue());
     }
 
+    #[test]
+    fn test_empty_doc() {
+        let s: String = "".to_owned();
+        YamlLoader::load_from_str(&s).unwrap();
+        let s: String = "---".to_owned();
+        assert_eq!(YamlLoader::load_from_str(&s).unwrap()[0], Yaml::Null);
+    }
+
     #[test]
     fn test_parser() {
         let s: String = "