exchange_rate: fix #5495

electrum/exchange_rate.py

@@ -615,11 +615,11 @@ class FxThread(ThreadJob):
         rate = self.exchange.historical_rate(self.ccy, d_t)
         # Frequently there is no rate for today, until tomorrow :)
         # Use spot quotes in that case
-        if rate == 'NaN' and (datetime.today().date() - d_t.date()).days <= 2:
+        if rate in ('NaN', None) and (datetime.today().date() - d_t.date()).days <= 2:
             rate = self.exchange.quotes.get(self.ccy, 'NaN')
-            if rate is None:
-                rate = 'NaN'
             self.history_used_spot = True
+        if rate is None:
+            rate = 'NaN'
         return Decimal(rate)
 
     def historical_value_str(self, satoshis, d_t):