Respond to currency changes.

app/Support/Http/Api/ExchangeRateConverter.php

@@ -167,7 +167,7 @@ class ExchangeRateConverter
 
         /** @var null|CurrencyExchangeRate $result */
         $result       = auth()->user()
-            ->currencyExchangeRates()
+            ?->currencyExchangeRates()
             ->where('from_currency_id', $from)
             ->where('to_currency_id', $to)
             ->where('date', '<=', $date)

app/Support/Models/AccountBalanceCalculator.php

@@ -243,7 +243,7 @@ class AccountBalanceCalculator
                 $object->balance = $balance[0];
                 $object->date    = $balance[1];
                 $object->date_tz = $balance[1]?->format('e');
-                $object->save();
+                $object->saveQuietly();
             }
         }
     }