fix exception when completing between arglist and body

pkg/analysis_server/lib/src/services/completion/optype.dart

Index: pkg/analysis_server/lib/src/services/completion/optype.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/optype.dart b/pkg/analysis_server/lib/src/services/completion/optype.dart
index 213ef10cb22aed51a1a4c1092ced4d4be5985a75..ad3c93044e9b907dc64516d1ba5f3355aab070bc 100644
--- a/pkg/analysis_server/lib/src/services/completion/optype.dart
+++ b/pkg/analysis_server/lib/src/services/completion/optype.dart
@@ -320,6 +320,9 @@ class _OpTypeAstVisitor extends GeneralizingAstVisitor {
   }
 
   @override
+  visitFunctionExpression(FunctionExpression node) {}
+
+  @override
   void visitFunctionTypeAlias(FunctionTypeAlias node) {
     if (identical(entity, node.returnType) ||
         identical(entity, node.name) && node.returnType == null) {