Fix opts.BaseUrl null ref (App Cast Gen)

Fixes #173

Author: Deadpikle

src/NetSparkle.Tools.AppCastGenerator/NetSparkle.Tools.AppCastGenerator.csproj

@@ -44,18 +44,18 @@
   </PropertyGroup>
   <PropertyGroup>
     <PostBuildEvent />
-    <AssemblyVersion>2.0.0.0</AssemblyVersion>
-    <FileVersion>2.0.0.0</FileVersion>
+    <AssemblyVersion>2.0.1.0</AssemblyVersion>
+    <FileVersion>2.0.1.0</FileVersion>
     <PackageId>NetSparkleUpdater.Tools.AppCastGenerator</PackageId>
-    <Version>2.0.0</Version>
+    <Version>2.0.1</Version>
     <Authors>Deadpikle</Authors>
     <PackageLicenseFile>LICENSE.md</PackageLicenseFile>
     <PackageProjectUrl>https://github.com/NetSparkleUpdater/NetSparkle</PackageProjectUrl>
     <PackageIcon>software-update-available.png</PackageIcon>
     <RepositoryUrl>https://github.com/NetSparkleUpdater/NetSparkle.git</RepositoryUrl>
     <RepositoryType>git</RepositoryType>
     <PackageTags>sparkle, netsparkle, update, software, updater, appcast, generate, software, app cast</PackageTags>
-    <PackageReleaseNotes>2.0.0: See https://github.com/NetSparkleUpdater/NetSparkle for all release information and to file issues/pull requests for this project.</PackageReleaseNotes>
+    <PackageReleaseNotes>2.0.1: See https://github.com/NetSparkleUpdater/NetSparkle for all release information and to file issues/pull requests for this project.</PackageReleaseNotes>
     <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
   </PropertyGroup>
   <ItemGroup>

src/NetSparkle.Tools.AppCastGenerator/Program.cs

@@ -248,9 +248,9 @@ static void Run(Options opts)
                     var itemTitle = string.IsNullOrWhiteSpace(productName) ? productVersion : productName + " " + productVersion;
 
                     var urlEncodedFileName = HttpUtility.UrlEncode(fileInfo.Name);
-                    var urlToUse = opts.BaseUrl.ToString().EndsWith("/")
-                        ? opts.BaseUrl.ToString()
-                        : opts.BaseUrl + "/";
+                    var urlToUse = !string.IsNullOrWhiteSpace(opts.BaseUrl?.ToString()) 
+                        ? (opts.BaseUrl.ToString().EndsWith("/") ? opts.BaseUrl.ToString() : opts.BaseUrl + "/") 
+                        : "";
                     if (opts.PrefixVersion)
                     {
                         urlToUse += $"{version}/";