should not type check null/undefined for non-required props (fix #2411)

Author: yyx990803

src/util/component.js

@@ -104,9 +104,12 @@ export function initProp (vm, prop, value) {
  */
 
 export function assertProp (prop, value) {
-  // if a prop is not provided and is not required,
-  // skip the check.
-  if (prop.raw === null && !prop.required) {
+  if (
+    !prop.options.required && ( // non-required
+      prop.raw === null ||      // abscent
+      value == null             // null or undefined
+    )
+  ) {
     return true
   }
   var options = prop.options

test/unit/specs/directives/internal/prop_spec.js

@@ -293,7 +293,7 @@ describe('prop', function () {
   })
 
   describe('assertions', function () {
-    function makeInstance (value, type, validator, coerce) {
+    function makeInstance (value, type, validator, coerce, required) {
       return new Vue({
         el: document.createElement('div'),
         template: '<test :test="val"></test>',
@@ -306,7 +306,8 @@ describe('prop', function () {
               test: {
                 type: type,
                 validator: validator,
-                coerce: coerce
+                coerce: coerce,
+                required: required
               }
             }
           }
@@ -415,6 +416,22 @@ describe('prop', function () {
       })
       expect(hasWarned('Missing required prop')).toBe(true)
     })
+
+    it('optional with type + null/undefined', function () {
+      makeInstance(undefined, String)
+      expect(getWarnCount()).toBe(0)
+      makeInstance(null, String)
+      expect(getWarnCount()).toBe(0)
+    })
+
+    it('required with type + null/undefined', function () {
+      makeInstance(undefined, String, null, null, true)
+      expect(getWarnCount()).toBe(1)
+      expect(hasWarned('Expected String')).toBe(true)
+      makeInstance(null, Boolean, null, null, true)
+      expect(getWarnCount()).toBe(2)
+      expect(hasWarned('Expected Boolean')).toBe(true)
+    })
   })
 
   it('alternative syntax', function () {