diff --git a/build.gradle b/build.gradle
index 4867a81c..254949e5 100644
--- a/build.gradle
+++ b/build.gradle
@@ -157,7 +157,6 @@ openapiProcessor {
         targetDir "$buildDir/generated/sources/openapi-javax"
         showWarnings true
         openApiNullable true
-        // generateAliasAsModel true
     }
 }
 sourceSets.main.java.srcDir 'build/generated/sources/openapi'
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/booking/item/HsBookingItemEntityPatcher.java b/src/main/java/net/hostsharing/hsadminng/hs/booking/item/HsBookingItemEntityPatcher.java
index 1905967b..8aa0e198 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/booking/item/HsBookingItemEntityPatcher.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/booking/item/HsBookingItemEntityPatcher.java
@@ -3,14 +3,10 @@ package net.hostsharing.hsadminng.hs.booking.item;
 import net.hostsharing.hsadminng.hs.booking.generated.api.v1.model.HsBookingItemPatchResource;
 import net.hostsharing.hsadminng.mapper.EntityPatcher;
 import net.hostsharing.hsadminng.mapper.OptionalFromJson;
-import org.apache.commons.lang3.tuple.ImmutablePair;
 
-import java.util.HashMap;
 import java.util.Map;
 import java.util.Optional;
 
-import static java.util.Arrays.stream;
-
 public class HsBookingItemEntityPatcher implements EntityPatcher<HsBookingItemPatchResource> {
 
     private final HsBookingItemEntity entity;
@@ -24,40 +20,19 @@ public class HsBookingItemEntityPatcher implements EntityPatcher<HsBookingItemPa
         OptionalFromJson.of(resource.getCaption())
                 .ifPresent(entity::setCaption);
         Optional.ofNullable(resource.getResources())
-                .ifPresent(r -> entity.getResources().patch(objectToMap(resource.getResources())));
+                .ifPresent(r -> entity.getResources().patch(castToKeyValueMap(resource.getResources())));
         OptionalFromJson.of(resource.getValidFrom())
                 .ifPresent(entity::setValidFrom);
         OptionalFromJson.of(resource.getValidTo())
                 .ifPresent(entity::setValidTo);
     }
 
-    static Map<String, Object> objectToMap(final Object obj) {
+    @SuppressWarnings("unchecked")
+    static Map<String, Object> castToKeyValueMap(final Object obj) {
         if (obj instanceof Map<?, ?>) {
-            return toKeyValueMap(obj);
+            return (Map<String, Object>) obj;
         }
-        return stream(obj.getClass().getDeclaredFields())
-                .map(field -> {
-                    try {
-                        field.setAccessible(true);
-                        return new ImmutablePair<>(field.getName(), field.get(obj));
-                    } catch (final IllegalAccessException exc) {
-                        throw new RuntimeException(exc);
-                    }
-                })
-                .reduce(
-                        new HashMap<>(),
-                        (map, pair) -> {
-                            map.put(pair.getKey(), pair.getValue());
-                            return map;
-                        },
-                        (map1, map2) -> {
-                            map1.putAll(map2);
-                            return map1;
-                        });
+        throw new ClassCastException("Map expected, but got: " + obj);
     }
 
-    @SuppressWarnings("unchecked")
-    private static Map<String, Object> toKeyValueMap(final Object obj) {
-        return (Map<String, Object>) obj;
-    }
 }
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/booking/item/HsBookingItemEntityPatcherUnitTest.java b/src/test/java/net/hostsharing/hsadminng/hs/booking/item/HsBookingItemEntityPatcherUnitTest.java
index dd3a59ee..9234a3ec 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/booking/item/HsBookingItemEntityPatcherUnitTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/booking/item/HsBookingItemEntityPatcherUnitTest.java
@@ -16,7 +16,7 @@ import java.util.Map;
 import java.util.UUID;
 import java.util.stream.Stream;
 
-import static net.hostsharing.hsadminng.hs.booking.item.HsBookingItemEntityPatcher.objectToMap;
+import static net.hostsharing.hsadminng.hs.booking.item.HsBookingItemEntityPatcher.castToKeyValueMap;
 import static net.hostsharing.hsadminng.hs.office.debitor.TestHsOfficeDebitor.TEST_DEBITOR;
 import static net.hostsharing.hsadminng.mapper.PatchMap.entry;
 import static net.hostsharing.hsadminng.mapper.PatchMap.patchMap;
@@ -72,7 +72,7 @@ class HsBookingItemEntityPatcherUnitTest extends PatchUnitTestBase<
         final var entity = new HsBookingItemEntity();
         entity.setUuid(INITIAL_BOOKING_ITEM_UUID);
         entity.setDebitor(TEST_DEBITOR);
-        entity.getResources().putAll(objectToMap(INITIAL_RESOURCES));
+        entity.getResources().putAll(castToKeyValueMap(INITIAL_RESOURCES));
         entity.setCaption(INITIAL_CAPTION);
         entity.setValidity(Range.closedInfinite(GIVEN_VALID_FROM));
         return entity;