Analysis Options error notifications.

pkg/analyzer/lib/source/analysis_options_provider.dart

Index: pkg/analyzer/lib/source/analysis_options_provider.dart
diff --git a/pkg/analyzer/lib/source/analysis_options_provider.dart b/pkg/analyzer/lib/source/analysis_options_provider.dart
index 2c5dfdcc49a9fe7b4f2533e0b45cb32ae899a2e9..29062a26a41de8dbc6aa34f3471f16d98ad893a7 100644
--- a/pkg/analyzer/lib/source/analysis_options_provider.dart
+++ b/pkg/analyzer/lib/source/analysis_options_provider.dart
@@ -33,12 +33,14 @@ class AnalysisOptionsProvider {
     if (optionsSource == null) {
       return options;
     }
-    var doc = loadYaml(optionsSource);
+    YamlNode doc = loadYamlNode(optionsSource);
+    // Empty options.
+    if (doc is YamlScalar && doc.value == null) {
+      return options;
+    }
     if ((doc != null) && (doc is! YamlMap)) {
       throw new OptionsFormatException(
-          'Bad options file format (expected map, got ${doc.runtimeType})\n'
-          'contents of options file:\n'
-          '$optionsSource\n',
+          'Bad options file format (expected map, got ${doc.runtimeType})',
           doc.span);
     }
     if (doc is YamlMap) {