mcp tool call: add dummy argument if there are no arguments given

Author: rainu

internal/mcp/client/tool_call.go

@@ -20,6 +20,11 @@ func CallTool(ctx context.Context, tp Transporter, toolName string, argsAsJson s
 	if err != nil {
 		return nil, fmt.Errorf("failed to unmarshal tool call arguments: %w", err)
 	}
+	if len(req.Params.Arguments) == 0 {
+		req.Params.Arguments = map[string]any{
+			"_": "_", // some tools require at least one argument, so we add a dummy one
+		}
+	}
 
 	execCtx, cancel := tp.GetTimeouts().ExecutionContext(ctx)
 	defer cancel()