correct behaviour when initialising date-picker with a empty string

src/components/date-picker/picker.vue

@@ -517,7 +517,7 @@
                         val = val.join(RANGE_SEPARATOR);
                         val = parser(val, this.format || DEFAULT_FORMATS[type]);
                     } else if (typeof val === 'string' && type.indexOf('time') !== 0 ){
-                        val = parser(val, this.format || DEFAULT_FORMATS[type]);
+                        val = parser(val, this.format || DEFAULT_FORMATS[type]) || val;
                     }
 
                     this.internalValue = val;

test/unit/specs/date-picker.spec.js

@@ -176,4 +176,19 @@ describe('DatePicker.vue', () => {
       });
     });
   });
+
+  it('should accept a empty string as input v-model value', done => {
+    vm = createVue({
+      template: '<date-picker v-model="value" type="date"></date-picker>',
+      data(){
+        return {value: ''};
+      }
+    });
+
+    vm.$nextTick(() => {
+      expect(vm.value).to.equal('');
+      done();
+    });
+  });
+
 });