fix(api): return value unchanged in toCurrency for null currencies

Prevents 'No exchange rate has been found for nullEUR' error logs when
toCurrency is called with a null or undefined source or target currency
(e.g. an account without a currency set).

Fixes ghostfolio/ghostfolio#6168

Signed-off-by: Rene Turcios <95189389+CloudCorpRecords@users.noreply.github.com>

apps/api/src/services/exchange-rate-data/exchange-rate-data.service.spec.ts

@@ -0,0 +1,42 @@
+import { ExchangeRateDataService } from './exchange-rate-data.service';
+
+describe('ExchangeRateDataService', () => {
+  let service: ExchangeRateDataService;
+
+  beforeEach(() => {
+    service = new ExchangeRateDataService(null, null, null, null);
+  });
+
+  describe('toCurrency', () => {
+    it('should return the value unchanged for a null source currency without logging an error', () => {
+      const loggerSpy = jest.spyOn(service['logger'], 'error');
+
+      const result = service.toCurrency(100, null as any, 'EUR');
+
+      expect(result).toEqual(100);
+      expect(loggerSpy).not.toHaveBeenCalled();
+    });
+
+    it('should return the value unchanged for an undefined source currency without logging an error', () => {
+      const loggerSpy = jest.spyOn(service['logger'], 'error');
+
+      const result = service.toCurrency(100, undefined as any, 'EUR');
+
+      expect(result).toEqual(100);
+      expect(loggerSpy).not.toHaveBeenCalled();
+    });
+
+    it('should return the value unchanged for a null target currency without logging an error', () => {
+      const loggerSpy = jest.spyOn(service['logger'], 'error');
+
+      const result = service.toCurrency(100, 'EUR', null as any);
+
+      expect(result).toEqual(100);
+      expect(loggerSpy).not.toHaveBeenCalled();
+    });
+
+    it('should return 0 for a value of 0', () => {
+      expect(service.toCurrency(0, 'USD', 'EUR')).toEqual(0);
+    });
+  });
+});

apps/api/src/services/exchange-rate-data/exchange-rate-data.service.ts

@@ -257,6 +257,13 @@ export class ExchangeRateDataService {
       return 0;
     }
 
+    if (!aFromCurrency || !aToCurrency) {
+      // The currency of the value is unknown (e.g. an account without a
+      // currency), so no conversion can be performed. Return the value
+      // unchanged instead of logging an error for a "null" currency.
+      return aValue;
+    }
+
     let factor: number;
 
     if (aFromCurrency === aToCurrency) {