fix(trend): pass empty dict to ccxt create_order for DCA adds

Gate build_gate_order_params returns {} which is falsy; params or None broke trend_market_add with NoneType is not iterable while first-leg place_exchange_order worked.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_trend_market_add_params.py

@@ -0,0 +1,28 @@
+"""趋势补仓下单：空 params 不得变成 None（ccxt 会报 not iterable）。"""
+from __future__ import annotations
+
+import unittest
+from unittest.mock import MagicMock
+
+from strategy_trend_exchange import trend_market_add
+
+
+class TestTrendMarketAddParams(unittest.TestCase):
+    def test_empty_gate_params_not_passed_as_none(self):
+        ex = MagicMock()
+        ex.create_order.return_value = {"id": "1", "average": 0.34}
+        app = MagicMock()
+        app.exchange = ex
+        app.ensure_markets_loaded = MagicMock()
+        app.build_gate_order_params = MagicMock(return_value={})
+        cfg = {"app_module": app}
+
+        trend_market_add(cfg, "ONDO/USDT:USDT", "long", 23, 10)
+
+        args = ex.create_order.call_args
+        self.assertEqual(args[0][5], {})
+        self.assertIsNotNone(args[0][5])
+
+
+if __name__ == "__main__":
+    unittest.main()