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:
         """

tests/strategy/test_interface.py

@@ -302,6 +302,13 @@ def test_populate_any_indicators(default_conf, testdatadir) -> None:
     assert len(processed['UNITTEST/BTC']) == 102  # partial candle was removed
 
 
+def test_freqai_not_initialized(default_conf) -> None:
+    strategy = StrategyResolver.load_strategy(default_conf)
+    strategy.ft_bot_start()
+    with pytest.raises(OperationalException, match=r'freqAI is not enabled\.'):
+        strategy.freqai.start()
+
+
 def test_advise_all_indicators_copy(mocker, default_conf, testdatadir) -> None:
     strategy = StrategyResolver.load_strategy(default_conf)
     aimock = mocker.patch('freqtrade.strategy.interface.IStrategy.advise_indicators')