fix show single command

Author: neuecc

src/ConsoleAppFramework/CommandHelpBuilder.cs

@@ -46,7 +46,7 @@ public string BuildHelpMessage(MethodInfo[] methodInfo, MethodInfo? defaultMetho
                 sb.Append(BuildHelpMessage(CreateCommandHelpDefinition(defaultMethod), showCommandName: false));
             }
 
-            if (methodInfo.Length > 1)
+            if ((defaultMethod == null && methodInfo.Length == 1) || methodInfo.Length > 1)
             {
                 // Display sub commands list.
                 sb.Append(BuildUsageMessage());
@@ -80,6 +80,12 @@ public string BuildHelpMessage(CommandHelpDefinition definition, bool showComman
                 sb.Append(BuildArgumentsMessage(definition));
                 sb.Append(BuildOptionsMessage(definition));
             }
+            else
+            {
+                sb.AppendLine("Options:");
+                sb.AppendLine("  ()");
+                sb.AppendLine();
+            }
 
             return sb.ToString();
         }

src/ConsoleAppFramework/ConsoleAppEngineHostBuilderExtensions.cs

@@ -143,7 +143,7 @@ IHostBuilder ConfigureEmptyService()
                 {
                     if (!hasHelp)
                     {
-                        Console.Write(new CommandHelpBuilder().BuildHelpMessage(methods, defaultMethod));
+                        Console.Write(new CommandHelpBuilder().BuildHelpMessage(methods, null));
                         ConfigureEmptyService();
                         return hostBuilder;
                     }