Improves options validation type safety (#24885).

pkg/analysis_server/lib/src/context_manager.dart

Index: pkg/analysis_server/lib/src/context_manager.dart
diff --git a/pkg/analysis_server/lib/src/context_manager.dart b/pkg/analysis_server/lib/src/context_manager.dart
index 272dafa90008dde32e97c6d4f9bd1a07b0519f40..a3fd86330797a4c620af5db5d437bd1e4e623fdb 100644
--- a/pkg/analysis_server/lib/src/context_manager.dart
+++ b/pkg/analysis_server/lib/src/context_manager.dart
@@ -505,8 +505,8 @@ class ContextManagerImpl implements ContextManager {
     }
 
     // Analysis options are processed 'in-line'.
-    YamlMap analyzer = options[AnalyzerOptions.analyzer];
-    if (analyzer == null) {
+    YamlNode analyzer = options[AnalyzerOptions.analyzer];
+    if (analyzer is! YamlMap) {
       // No options for analyzer.
       return;
     }