Correctly check if no trend signals are defined

core/lib/market.py

@@ -407,7 +407,7 @@ def execute_strategy(callback, strategy, func):
         return
 
     # Check if we are trading against the trend
-    if strategy.trend_signals is not None:
+    if strategy.trend_signals.exists():
         if strategy.trends is None:
             log.debug("Refusing to trade with no trend signals received")
             return