Simplify liquidation price structure, improve test cov

freqtrade/exchange/exchange.py

@@ -2611,8 +2611,9 @@ class Exchange:
             return None
         elif (self.trading_mode != TradingMode.FUTURES):
             raise OperationalException(
-                f"{self.name} does not support {self.margin_mode.value} {self.trading_mode.value}")
+                f"{self.name} does not support {self.margin_mode} {self.trading_mode}")
 
+        isolated_liq = None
         if self._config['dry_run'] or not self.exchange_has("fetchPositions"):
 
             isolated_liq = self.dry_run_liquidation_price(
@@ -2630,8 +2631,6 @@ class Exchange:
             if len(positions) > 0:
                 pos = positions[0]
                 isolated_liq = pos['liquidationPrice']
-            else:
-                return None
 
         if isolated_liq:
             buffer_amount = abs(open_rate - isolated_liq) * self.liquidation_buffer

tests/exchange/test_exchange.py

@@ -5000,6 +5000,28 @@ def test_get_liquidation_price1(mocker, default_conf):
     )
     assert liq_price == 17.540699999999998
 
+    api_mock.fetch_positions = MagicMock(return_value=[])
+    exchange = get_patched_exchange(mocker, default_conf, api_mock)
+    liq_price = exchange.get_liquidation_price(
+        pair='NEAR/USDT:USDT',
+        open_rate=18.884,
+        is_short=False,
+        amount=0.8,
+        stake_amount=18.884 * 0.8,
+    )
+    assert liq_price is None
+    default_conf['trading_mode'] = 'margin'
+
+    exchange = get_patched_exchange(mocker, default_conf, api_mock)
+    with pytest.raises(OperationalException, match=r'.*does not support .* margin'):
+        exchange.get_liquidation_price(
+            pair='NEAR/USDT:USDT',
+            open_rate=18.884,
+            is_short=False,
+            amount=0.8,
+            stake_amount=18.884 * 0.8,
+        )
+
 
 @pytest.mark.parametrize('liquidation_buffer', [0.0, 0.05])
 @pytest.mark.parametrize(