diff --git a/user-manager-server/src/main/java/de/ozgcloud/user/UserResourceMapper.java b/user-manager-server/src/main/java/de/ozgcloud/user/UserResourceMapper.java
index ba7ca20c6921171be74ff1a758202e4cb35b5e8a..65826fba33a2f1ba591163c88bcffd77431bea42 100644
--- a/user-manager-server/src/main/java/de/ozgcloud/user/UserResourceMapper.java
+++ b/user-manager-server/src/main/java/de/ozgcloud/user/UserResourceMapper.java
@@ -26,12 +26,12 @@ package de.ozgcloud.user;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Date;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
+import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 import jakarta.inject.Inject;
@@ -79,14 +79,13 @@ public abstract class UserResourceMapper {
 
 	Set<String> mapOrganisationsEinheitIds(UserResource userRes) {
 		var groups = userRes.groups();
-		var organisationsEinheitIds = Stream.concat(
-				getOrganisationsEinheitIdsFromGroups(groups),
-				getOrganisationsEinheitIdsFromUser(userRes)
-			)
+		return Stream.concat(
+						getOrganisationsEinheitIdsFromGroups(groups),
+						getOrganisationsEinheitIdsFromUser(userRes)
+				)
 				.filter(Objects::nonNull)
 				.filter(oeId -> !oeId.isBlank())
-				.toList();
-		return new HashSet<>(organisationsEinheitIds);
+				.collect(Collectors.toSet());
 	}
 
 	private Stream<String> getOrganisationsEinheitIdsFromGroups(List<GroupRepresentation> groups) {
@@ -99,8 +98,8 @@ public abstract class UserResourceMapper {
 	}
 
 	private Stream<String> getOrganisationsEinheitIdsFromUser(UserResource userRes) {
-		return Optional.ofNullable(userRes.toRepresentation().getAttributes().get(properties.organisationsEinheitIdKey()))
-				.orElse(List.of())
+		return Optional.ofNullable(getUserAttributes(userRes).get(properties.organisationsEinheitIdKey()))
+				.orElse(Collections.emptyList())
 				.stream();
 	}
 
@@ -159,4 +158,8 @@ public abstract class UserResourceMapper {
 		return String.join(" ", Stream.of(userRes.toRepresentation().getLastName(), userRes.toRepresentation().getFirstName())
 				.filter(Objects::nonNull).toArray(String[]::new));
 	}
+
+	private Map<String, List<String>> getUserAttributes(UserResource userResource) {
+		return Optional.ofNullable(userResource.toRepresentation().getAttributes()).orElse(Map.of());
+	}
 }
diff --git a/user-manager-server/src/test/java/de/ozgcloud/user/GroupRepresentationTestFactory.java b/user-manager-server/src/test/java/de/ozgcloud/user/GroupRepresentationTestFactory.java
index 617f124641d8366a8785c3951a3a6ea5fed7c201..ef6f392a0ca35993bd50422df19a42ac3a69367b 100644
--- a/user-manager-server/src/test/java/de/ozgcloud/user/GroupRepresentationTestFactory.java
+++ b/user-manager-server/src/test/java/de/ozgcloud/user/GroupRepresentationTestFactory.java
@@ -35,16 +35,12 @@ class GroupRepresentationTestFactory {
 		return group;
 	}
 
-	public static GroupRepresentation createByPathAndOrganisationEinheitId(String groupPath, String organisationEinheitId) {
-		return createByPathAndOrganisationEinheitIds(groupPath, List.of(organisationEinheitId));
-	}
-
-	public static GroupRepresentation createByPathAndOrganisationEinheitIds(String groupPath, List<String> organisationEinheitIds) {
+	public static GroupRepresentation createByPathAndOrganisationEinheitIds(String groupPath, String... organisationEinheitIds) {
 		var groupRepresentation = new GroupRepresentation();
 		groupRepresentation.setName(groupPath);
 		groupRepresentation.setPath(groupPath);
 		groupRepresentation.setAttributes(Map.of(UserResourceMapperTest.ORGANISATIONS_EINHEIT_ID_KEY,
-				organisationEinheitIds));
+				List.of(organisationEinheitIds)));
 		return groupRepresentation;
 	}
 }
diff --git a/user-manager-server/src/test/java/de/ozgcloud/user/UserResourceMapperTest.java b/user-manager-server/src/test/java/de/ozgcloud/user/UserResourceMapperTest.java
index ef790b9a137fd722f8a67552fa915e2ed28a8055..40a505bec362d80c4ef168875cec373729a453de 100644
--- a/user-manager-server/src/test/java/de/ozgcloud/user/UserResourceMapperTest.java
+++ b/user-manager-server/src/test/java/de/ozgcloud/user/UserResourceMapperTest.java
@@ -36,7 +36,6 @@ import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.keycloak.admin.client.resource.RealmResource;
 import org.keycloak.admin.client.resource.RoleMappingResource;
-import org.keycloak.admin.client.resource.RoleScopeResource;
 import org.keycloak.admin.client.resource.UserResource;
 import org.keycloak.representations.idm.ClientMappingsRepresentation;
 import org.keycloak.representations.idm.GroupRepresentation;
@@ -79,7 +78,7 @@ class UserResourceMapperTest {
 			when(properties.organisationsEinheitIdKey()).thenReturn("organisationseinheitId");
 			when(properties.client()).thenReturn("alfa");
 			when(realm.getGroupByPath(GROUP_1_PATH))
-					.thenReturn(GroupRepresentationTestFactory.createByPathAndOrganisationEinheitId(GROUP_1_PATH, ORGANISATIONS_EINHEIT_ID_1));
+					.thenReturn(GroupRepresentationTestFactory.createByPathAndOrganisationEinheitIds(GROUP_1_PATH, ORGANISATIONS_EINHEIT_ID_1));
 			when(properties.ldapIdKey()).thenReturn("LDAP_ID");
 			when(properties.organisationsEinheitIdKey()).thenReturn("organisationseinheitId");
 			when(properties.client()).thenReturn("alfa");
@@ -148,23 +147,6 @@ class UserResourceMapperTest {
 			verify(mapper).mapOrganisationsEinheitIds(userResource);
 		}
 
-		@Test
-		void shouldMapMultipleOrganisationsEinheitIds() {
-			var groupRepresentation = GroupRepresentationTestFactory.createByPathAndOrganisationEinheitId(GROUP_2_PATH,
-					ORGANISATIONS_EINHEIT_ID_2);
-			when(realm.getGroupByPath(GROUP_2_PATH)).thenReturn(groupRepresentation);
-
-			var user = toKopUser(buildUserResourceWithGroups());
-
-			assertThat(user.getOrganisationsEinheitIds()).isNotEmpty().hasSize(2).contains(ORGANISATIONS_EINHEIT_ID_2);
-		}
-
-		private UserResource buildUserResourceWithGroups() {
-			return UserResourceTestFactory.createWithGroups(List.of(
-					GroupRepresentationTestFactory.createGroup(UserResourceMapperTest.GROUP_1_PATH),
-					GroupRepresentationTestFactory.createGroup(UserResourceMapperTest.GROUP_2_PATH)));
-		}
-
 		@Test
 		void shouldMapRoles() {
 			var user = toKopUser();
@@ -209,11 +191,9 @@ class UserResourceMapperTest {
 
 		static final String ORGANISATIONS_EINHEIT_ID_3 = "6287";
 		private final GroupRepresentation group1 = GroupRepresentationTestFactory.createByPathAndOrganisationEinheitIds(
-				GROUP_1_PATH, List.of(ORGANISATIONS_EINHEIT_ID_1, ORGANISATIONS_EINHEIT_ID_3));
-		private final GroupRepresentation group2 = GroupRepresentationTestFactory.createByPathAndOrganisationEinheitId(
+				GROUP_1_PATH, ORGANISATIONS_EINHEIT_ID_1, ORGANISATIONS_EINHEIT_ID_3);
+		private final GroupRepresentation group2 = GroupRepresentationTestFactory.createByPathAndOrganisationEinheitIds(
 				GROUP_2_PATH, ORGANISATIONS_EINHEIT_ID_2);
-		private final Map<String, List<String>> attributes = Map.of(
-				ORGANISATIONS_EINHEIT_ID_KEY, List.of(ORGANISATIONS_EINHEIT_ID_1, ORGANISATIONS_EINHEIT_ID_2));
 
 		@BeforeEach
 		void beforeEach() {
@@ -238,11 +218,16 @@ class UserResourceMapperTest {
 
 			var result = mapper.mapOrganisationsEinheitIds(userResource);
 
-			assertThat(result).containsExactlyInAnyOrder(ORGANISATIONS_EINHEIT_ID_1, ORGANISATIONS_EINHEIT_ID_2, ORGANISATIONS_EINHEIT_ID_3);
+			assertThat(result).containsExactlyInAnyOrder(
+					ORGANISATIONS_EINHEIT_ID_1,
+					ORGANISATIONS_EINHEIT_ID_2,
+					ORGANISATIONS_EINHEIT_ID_3
+			);
 		}
 
 		@Test
 		void shouldMapOrganisationsEinheitIdsFromUser() {
+			var attributes = Map.of(ORGANISATIONS_EINHEIT_ID_KEY, List.of(ORGANISATIONS_EINHEIT_ID_1, ORGANISATIONS_EINHEIT_ID_2));
 			userResource = UserResourceTestFactory.createWithAttributes(attributes);
 
 			var result = mapper.mapOrganisationsEinheitIds(userResource);