Repository: urlaubsverwaltung/urlaubsverwaltung (java)
Issue: Fehler bei Anfrage von Feiertagen ohne Feiertagsregelung
**Describe the bug**
Eine Seite in der UV möchte aufgerufen werden, keine Feiertagsregelung ist hinterlegt. Somit wird ein immutable Set verwenden und dieses kann keine Einträge hinzufügen. Fehler wird geworfen. 

```
java.lang.UnsupportedOperationException
	at java.base/java.util.ImmutableCollections.uoe(ImmutableCollections.java:142)
	at java.base/java.util.ImmutableCollections$AbstractImmutableCollection.add(ImmutableCollections.java:147)
	at org.synyx.urlaubsverwaltung.publicholiday.PublicHolidaysServiceImpl.getHolidays(PublicHolidaysServiceImpl.java:101)
	at org.synyx.urlaubsverwaltung.publicholiday.PublicHolidaysServiceImpl.getPublicHolidays(PublicHolidaysServiceImpl.java:69)
	at org.synyx.urlaubsverwaltung.publicholiday.PublicHolidaysServiceImpl.getPublicHolidays(PublicHolidaysServiceImpl.java:63)
	at org.synyx.urlaubsverwaltung.publicholiday.PublicHolidaysServiceImplTest.ensureGetPublicHolidaysReturnsWhenPersonHasNoPublicHolidaysDefined(PublicHolidaysServiceImplTest.java:218)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
``
Pull request description: Fix immutable Set in public holiday
If no public holidays are in use, and they get called, the code cannot add further public holiday because the set is immutable.

closes #4999 

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Patch:
diff --git a/src/main/java/org/synyx/urlaubsverwaltung/publicholiday/PublicHolidaysServiceImpl.java b/src/main/java/org/synyx/urlaubsverwaltung/publicholiday/PublicHolidaysServiceImpl.java
index 1f12380ee..0b1731132 100644
--- a/src/main/java/org/synyx/urlaubsverwaltung/publicholiday/PublicHolidaysServiceImpl.java
+++ b/src/main/java/org/synyx/urlaubsverwaltung/publicholiday/PublicHolidaysServiceImpl.java
@@ -13,6 +13,7 @@ import org.synyx.urlaubsverwaltung.workingtime.WorkingTimeSettings;
 
 import java.time.LocalDate;
 import java.time.Month;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
@@ -90,7 +91,7 @@ public class PublicHolidaysServiceImpl implements PublicHolidaysService {
 
         final Set<Holiday> holidays = getHolidayManager(federalState)
             .map(holidayManager -> holidayManager.getHolidays(from, to, PUBLIC_HOLIDAY, federalState.getCodes()))
-            .orElseGet(Set::of);
+            .orElseGet(HashSet::new);
 
         final DateRange requestRange = new DateRange(from, to);
 


Test patch:
diff --git a/src/test/java/org/synyx/urlaubsverwaltung/publicholiday/PublicHolidaysServiceImplTest.java b/src/test/java/org/synyx/urlaubsverwaltung/publicholiday/PublicHolidaysServiceImplTest.java
index e77281536..a46f44129 100644
--- a/src/test/java/org/synyx/urlaubsverwaltung/publicholiday/PublicHolidaysServiceImplTest.java
+++ b/src/test/java/org/synyx/urlaubsverwaltung/publicholiday/PublicHolidaysServiceImplTest.java
@@ -33,6 +33,7 @@ import static org.mockito.Mockito.when;
 import static org.synyx.urlaubsverwaltung.workingtime.FederalState.GERMANY_BADEN_WUERTTEMBERG;
 import static org.synyx.urlaubsverwaltung.workingtime.FederalState.GERMANY_BAYERN_MUENCHEN;
 import static org.synyx.urlaubsverwaltung.workingtime.FederalState.GERMANY_BERLIN;
+import static org.synyx.urlaubsverwaltung.workingtime.FederalState.NONE;
 
 @ExtendWith(MockitoExtension.class)
 class PublicHolidaysServiceImplTest {
@@ -209,6 +210,19 @@ class PublicHolidaysServiceImplTest {
             new PublicHoliday(LocalDate.of(2023, DECEMBER, 31), null, null));
     }
 
+    @Test
+    void ensureGetPublicHolidaysReturnsWhenPersonHasNoPublicHolidaysDefined() {
+
+        when(settingsService.getSettings()).thenReturn(new Settings());
+
+        final List<PublicHoliday> publicHolidays = sut.getPublicHolidays(of(2020, JANUARY, 1), of(2023, DECEMBER, 31), NONE);
+
+        assertThat(publicHolidays).contains(
+            new PublicHoliday(LocalDate.of(2020, DECEMBER, 31), null, null),
+            new PublicHoliday(LocalDate.of(2021, DECEMBER, 31), null, null),
+            new PublicHoliday(LocalDate.of(2023, DECEMBER, 31), null, null));
+    }
+
     private HolidayManager getHolidayManager() {
         return HolidayManager.getInstance(ManagerParameters.create(HolidayCalendar.GERMANY));
     }