Convert nan to None in get_signal.

freqtrade/strategy/interface.py

@@ -654,6 +654,9 @@ class IStrategy(ABC, HyperStrategyMixin):
 
         buy_tag = latest.get(SignalTagType.BUY_TAG.value, None)
         exit_tag = latest.get(SignalTagType.EXIT_TAG.value, None)
+        # Tags can be None, which does not resolve to False.
+        buy_tag = buy_tag if isinstance(buy_tag, str) else None
+        exit_tag = exit_tag if isinstance(exit_tag, str) else None
 
         logger.debug('trigger: %s (pair=%s) buy=%s sell=%s',
                      latest['date'], pair, str(buy), str(sell))

tests/strategy/test_interface.py

@@ -36,6 +36,10 @@ def test_returns_latest_signal(ohlcv_history):
     mocked_history = ohlcv_history.copy()
     mocked_history['sell'] = 0
     mocked_history['buy'] = 0
+    # Set tags in lines that don't matter to test nan in the sell line
+    mocked_history.loc[0, 'buy_tag'] = 'wrong_line'
+    mocked_history.loc[0, 'exit_tag'] = 'wrong_line'
+
     mocked_history.loc[1, 'sell'] = 1
 
     assert _STRATEGY.get_signal('ETH/BTC', '5m', mocked_history) == (False, True, None, None)