Fix NullReferenceException when NuGet sources have leading whitespace

Co-authored-by: marcpopMSFT <[email protected]>

Author: Copilot

src/Cli/dotnet/NugetPackageDownloader/NuGetPackageDownloader.cs

@@ -355,7 +355,7 @@ private IEnumerable<PackageSource> LoadOverrideSources(PackageSourceLocation pac
                 continue;
             }
 
-            PackageSource packageSource = new(source);
+            PackageSource packageSource = new(source.Trim());
             if (packageSource.TrySourceAsUri == null)
             {
                 _verboseLogger.LogWarning(string.Format(
@@ -418,7 +418,7 @@ private List<PackageSource> LoadDefaultSources(PackageId packageId, PackageSourc
                     continue;
                 }
 
-                PackageSource packageSource = new(source);
+                PackageSource packageSource = new(source.Trim());
                 if (packageSource.TrySourceAsUri == null)
                 {
                     _verboseLogger.LogWarning(string.Format(

test/Microsoft.DotNet.PackageInstall.Tests/NuGetPackageInstallerTests.cs

@@ -59,6 +59,17 @@ public async Task GivenASourceInstallSucceeds()
             packagePath.Should().Contain(_tempDirectory.Value, "Package should be downloaded to the input folder");
         }
 
+        [Fact]
+        public async Task GivenSourceWithLeadingWhitespaceInstallSucceeds()
+        {
+            string packagePath = await _installer.DownloadPackageAsync(
+                TestPackageId,
+                new NuGetVersion(TestPackageVersion),
+                new PackageSourceLocation(sourceFeedOverrides: new[] { " " + GetTestLocalFeedPath() })); // Leading space
+            File.Exists(packagePath).Should().BeTrue();
+            packagePath.Should().Contain(_tempDirectory.Value, "Package should be downloaded to the input folder");
+        }
+
         [Fact]
         public async Task GivenAFailedSourceItShouldError()
         {
@@ -228,6 +239,19 @@ public async Task WhenPassedIncludePreviewItInstallSucceeds()
                 "Package should download higher package version");
         }
 
+        [Fact]
+        public async Task GivenAdditionalSourceWithLeadingWhitespaceInstallSucceeds()
+        {
+            string getTestLocalFeedPath = GetTestLocalFeedPath();
+            string relativePath = Path.GetRelativePath(Environment.CurrentDirectory, getTestLocalFeedPath);
+            string packagePath = await _installer.DownloadPackageAsync(
+                TestPackageId,
+                new NuGetVersion(TestPackageVersion),
+                new PackageSourceLocation(additionalSourceFeeds: new[] { " " + relativePath })); // Leading space
+            File.Exists(packagePath).Should().BeTrue();
+            packagePath.Should().Contain(_tempDirectory.Value, "Package should be downloaded to the input folder");
+        }
+
         [WindowsOnlyFact]
         public async Task GivenANonSignedSdkItShouldPrintMessageOnce()
         {