Report Fix uncorrect '0' receive by binders if html attribute is not …

spec/rivets/binders.js

@@ -184,4 +184,25 @@ describe("Rivets.binders", function() {
       Should(fragment.childNodes.length).be.exactly(1);
     });
   });
+
+  describe("Custom binder with no attribute value", function() {
+    rivets.binders["custom-binder"] = function(el, value) {
+      el.innerHTML = "received " + value;
+    };
+    beforeEach(function() {
+      el = document.createElement("div");
+    });
+
+    it("receives undefined when html attribute is not specified", function() {
+      el.innerHTML = "<div rv-custom-binder></div>";
+      var view = rivets.bind(el);
+      Should(el.children[0].innerHTML).be.exactly('received undefined');
+    });
+
+    it("receives undefined when html attribute is not specified", function() {
+      el.innerHTML = "<div rv-custom-binder=''></div>";
+      var view = rivets.bind(el);
+      Should(el.children[0].innerHTML).be.exactly('received undefined');
+    });
+  });
 });

src/parsers.js

@@ -18,6 +18,9 @@ export function parseType(string) {
     value = null
   } else if (string === 'undefined') {
     value = undefined
+  } else if (string === '') {
+    // string==='' means the Html attribute is empty, binder should receive undefined 
+    value = undefined
   } else if (isNaN(Number(string)) === false) {
     value = Number(string)
   } else {