fix: skip func body if not exists

LanguageRecogniser/Cpp/CppActivityDiagramVisitor.cs

@@ -99,15 +99,18 @@ public class CppActivityDiagramVisitor : CPP14ParserBaseVisitor<object>
 
     public override object VisitCompoundStatement(CPP14Parser.CompoundStatementContext context)
     {
-        foreach (var statement in context.statementSeq().statement())
+        if(context.statementSeq() != null)
         {
-            var text = Visit(statement);
-            
-            if (text != null)
+            foreach (var statement in context.statementSeq().statement())
             {
-                var pop = _decisionBuilderStack.Pop();
-                var push = pop.Item1.AddAction(text.ToString(), pop.Item2.Peek());
-                _decisionBuilderStack.Push((push, pop.Item2));
+                var text = Visit(statement);
+            
+                if (text != null)
+                {
+                    var pop = _decisionBuilderStack.Pop();
+                    var push = pop.Item1.AddAction(text.ToString(), pop.Item2.Peek());
+                    _decisionBuilderStack.Push((push, pop.Item2));
+                }
             }
         }
         return null;