Fix problem when no experimental dict is available

freqtrade/optimize/hyperopt.py

@@ -153,6 +153,9 @@ class Hyperopt(Backtesting):
             spaces += self.custom_hyperopt.indicator_space()
         if self.has_space('sell'):
             spaces += self.custom_hyperopt.sell_indicator_space()
+            # Make sure experimental is enabled
+            if 'experimental' not in self.config:
+                self.config['experimental'] = {}
             self.config['experimental']['use_sell_signal'] = True
         if self.has_space('roi'):
             spaces += self.custom_hyperopt.roi_space()

freqtrade/tests/optimize/test_hyperopt.py

@@ -312,6 +312,15 @@ def test_generate_optimizer(mocker, default_conf) -> None:
         'mfi-enabled': False,
         'rsi-enabled': False,
         'trigger': 'macd_cross_signal',
+        'sell-adx-value': 0,
+        'sell-fastd-value': 75,
+        'sell-mfi-value': 0,
+        'sell-rsi-value': 0,
+        'sell-adx-enabled': False,
+        'sell-fastd-enabled': True,
+        'sell-mfi-enabled': False,
+        'sell-rsi-enabled': False,
+        'sell-trigger': 'macd_cross_signal',
         'roi_t1': 60.0,
         'roi_t2': 30.0,
         'roi_t3': 20.0,