fix exceptions when completing other edge cases

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 ad3c93044e9b907dc64516d1ba5f3355aab070bc..83ef718627f1a8de62735ae549d78f596f61f2f7 100644
--- a/pkg/analysis_server/lib/src/services/completion/optype.dart
+++ b/pkg/analysis_server/lib/src/services/completion/optype.dart
@@ -320,7 +320,10 @@ class _OpTypeAstVisitor extends GeneralizingAstVisitor {
   }
 
   @override
-  visitFunctionExpression(FunctionExpression node) {}
+  void visitFunctionExpression(FunctionExpression node) {}
+
+  @override
+  void visitFunctionExpressionInvocation(FunctionExpressionInvocation node) {}
 
   @override
   void visitFunctionTypeAlias(FunctionTypeAlias node) {
@@ -435,6 +438,12 @@ class _OpTypeAstVisitor extends GeneralizingAstVisitor {
   }
 
   @override
+  void visitPostfixExpression(PostfixExpression node) {
+    optype.includeReturnValueSuggestions = true;
+    optype.includeTypeNameSuggestions = true;
+  }
+
+  @override
   void visitPrefixedIdentifier(PrefixedIdentifier node) {
     if (identical(entity, node.identifier)) {
       optype.includeInvocationSuggestions = true;
@@ -499,6 +508,12 @@ class _OpTypeAstVisitor extends GeneralizingAstVisitor {
   }
 
   @override
+  void visitThrowExpression(ThrowExpression node) {
+    optype.includeReturnValueSuggestions = true;
+    optype.includeTypeNameSuggestions = true;
+  }
+
+  @override
   void visitTypeArgumentList(TypeArgumentList node) {
     NodeList<TypeName> arguments = node.arguments;
     for (TypeName typeName in arguments) {