Merge branch 'dev-v7' into 7.3.0

Conflicts:
	src/Umbraco.Tests/Scheduling/BackgroundTaskRunnerTests.cs
	src/Umbraco.Web/PublishedCache/XmlPublishedCache/XmlCacheFilePersister.cs
	src/Umbraco.Web/Scheduling/LogScrubber.cs
	src/Umbraco.Web/Umbraco.Web.csproj
	src/Umbraco.Web/umbraco.presentation/content.cs

src/Umbraco.Web.UI.Client/src/common/services/mediahelper.service.js

@@ -327,6 +327,11 @@ function mediaHelper(umbRequestHelper) {
          * @param {string} imagePath Image path, ex: /media/1234/my-image.jpg
          */
         detectIfImageByExtension: function (imagePath) {
+
+            if (!imagePath) {
+                return false;
+            }
+            
             var lowered = imagePath.toLowerCase();
             var ext = lowered.substr(lowered.lastIndexOf(".") + 1);
             return ("," + Umbraco.Sys.ServerVariables.umbracoSettings.imageFileTypes + ",").indexOf("," + ext + ",") !== -1;