Fixes: U4-3350 Content Validation: Can't get rid of DateTime error

src/Umbraco.Core/PropertyEditors/PropertyValueEditor.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Xml.Linq;
 using Newtonsoft.Json;
+using Umbraco.Core.Logging;
 using Umbraco.Core.Manifest;
 using Umbraco.Core.Models;
 using Umbraco.Core.Models.Editors;
@@ -223,7 +224,8 @@ namespace Umbraco.Core.PropertyEditors
             var result = TryConvertValueToCrlType(editorValue.Value);
             if (result.Success == false)
             {
-                throw new InvalidOperationException("The value " + editorValue + " cannot be converted to the type " + GetDatabaseType());
+                LogHelper.Warn<PropertyValueEditor>("The value " + editorValue.Value + " cannot be converted to the type " + GetDatabaseType());
+                return null;
             }
             return result.Result;
         }

src/Umbraco.Web.UI.Client/src/common/directives/validation/valserver.directive.js

@@ -26,17 +26,20 @@ function valServer(serverValidationManager) {
                 }
             }            
 
-            //subscribe to the changed event of the view model. This is required because when we
+            //Need to watch the value model for it to change, previously we had  subscribed to 
+            //ctrl.$viewChangeListeners but this is not good enough if you have an editor that
+            // doesn't specifically have a 2 way ng binding. This is required because when we
             // have a server error we actually invalidate the form which means it cannot be 
             // resubmitted. So once a field is changed that has a server error assigned to it
             // we need to re-validate it for the server side validator so the user can resubmit
             // the form. Of course normal client-side validators will continue to execute.
-            //TODO: Should we be using $render here instead?
-            ctrl.$viewChangeListeners.push(function () {
+            scope.$watch(function() {
+                return ctrl.$modelValue;
+            }, function (newValue) {
                 if (ctrl.$invalid) {
                     ctrl.$setValidity('valServer', true);
                 }
-            });
+            });            
             
             //subscribe to the server validation changes
             serverValidationManager.subscribe(currentProperty.alias, fieldName, function (isValid, propertyErrors, allErrors) {

src/Umbraco.Web.UI.Client/src/views/propertyeditors/datepicker/datepicker.controller.js

@@ -1,5 +1,5 @@
 angular.module("umbraco").controller("Umbraco.PropertyEditors.DatepickerController",
-    function ($scope, notificationsService, assetsService) {
+    function ($scope, notificationsService, assetsService, angularHelper) {
 
         //setup the default config
         var config = {
@@ -12,17 +12,19 @@ angular.module("umbraco").controller("Umbraco.PropertyEditors.DatepickerControll
         //map back to the model
         $scope.model.config = config;
 
-        function applyDate(e){
+        function applyDate(e) {
+
+            angularHelper.safeApply($scope, function() {
                 // when a date is changed, update the model
                 if (e.localDate) {
                     if ($scope.model.config.format == "yyyy-MM-dd HH:mm:ss") {
-                        $scope.$apply(function(){
-                            $scope.model.value = e.localDate.toIsoDateTimeString();
-                        });
-                    }else{
+                        $scope.model.value = e.localDate.toIsoDateTimeString();
+                    }
+                    else {
                         $scope.model.value = e.localDate.toIsoDateString();
                     }
                 }
+            });
         }
 
         assetsService.loadJs(

src/Umbraco.Web/PropertyEditors/DateTimeValidator.cs

@@ -14,8 +14,14 @@ namespace Umbraco.Web.PropertyEditors
     {
         public IEnumerable<ValidationResult> Validate(object value, PreValueCollection preValues, PropertyEditor editor)
         {
+            //don't validate if empty
+            if (value == null || value.ToString().IsNullOrWhiteSpace())
+            {
+                yield break;
+            }
+
             DateTime dt;
-            if (value != null &&  DateTime.TryParse(value.ToString(), out dt) == false)
+            if (DateTime.TryParse(value.ToString(), out dt) == false)
             {
                 yield return new ValidationResult(string.Format("The string value {0} cannot be parsed into a DateTime", value),
                                                   new[]