Fix some issues with options handling

pkg/analyzer_cli/lib/src/driver.dart

Index: pkg/analyzer_cli/lib/src/driver.dart
diff --git a/pkg/analyzer_cli/lib/src/driver.dart b/pkg/analyzer_cli/lib/src/driver.dart
index 1a22de5803f31170953917c0d9b50570305f6efa..5c34be4c25570b7071d0f595db5fc77ef1b8cafb 100644
--- a/pkg/analyzer_cli/lib/src/driver.dart
+++ b/pkg/analyzer_cli/lib/src/driver.dart
@@ -786,7 +786,9 @@ class Driver implements CommandLineStarter {
     contextOptions.hint = !options.disableHints;
     contextOptions.generateImplicitErrors = options.showPackageWarnings;
     contextOptions.generateSdkErrors = options.showSdkWarnings;
-    contextOptions.enableAssertInitializer = options.enableAssertInitializer;
+    if (options.enableAssertInitializer != null) {
+      contextOptions.enableAssertInitializer = options.enableAssertInitializer;
+    }
 
     return contextOptions;
   }