Graciously fail if strategy has freqAI code, but freqAI is not enabled.

freqtrade/strategy/interface.py

@@ -152,6 +152,13 @@ class IStrategy(ABC, HyperStrategyMixin):
 
             self.freqai = FreqaiModelResolver.load_freqaimodel(self.config)
             self.freqai_info = self.config["freqai"]
+        else:
+            # Gracious failures if freqAI is disabled but "start" is called.
+            class DummyClass():
+                def start(self, *args, **kwargs):
+                    raise OperationalException(
+                        'freqAI is not enabled. Please enable it in your config to use this strategy.')
+            self.freqai = DummyClass()  # type: ignore
 
     def ft_bot_start(self, **kwargs) -> None:
         """