fix failing bazel workspace relative path test

pkg/analyzer_cli/lib/src/options.dart

Index: pkg/analyzer_cli/lib/src/options.dart
diff --git a/pkg/analyzer_cli/lib/src/options.dart b/pkg/analyzer_cli/lib/src/options.dart
index f93d5f6e62ffe6cc4769df893ccf81d87f3f5bcd..aab9ddf32158c3dbfb789cf71cbd6abee5bc21cd 100644
--- a/pkg/analyzer_cli/lib/src/options.dart
+++ b/pkg/analyzer_cli/lib/src/options.dart
@@ -250,10 +250,12 @@ class CommandLineOptions {
     if (options.buildModePersistentWorker && !options.buildMode) {
       printAndFail('The option --persisten_worker can be used only '
           'together with --build-mode.');
+      return null; // Only reachable in testing.
     }
     if (options.buildSummaryOnlyDiet && !options.buildSummaryOnly) {
       printAndFail('The option --build-summary-only-diet can be used only '
           'together with --build-summary-only.');
+      return null; // Only reachable in testing.
     }
 
     return options;