Bug in LocationConstraint: fix us-east-1 handling

Serialization would always fail.

Author: afranken

server/src/main/java/com/adobe/testing/s3mock/dto/RegionSerializer.java

@@ -33,7 +33,8 @@ public void serialize(Region value, JsonGenerator gen, SerializerProvider serial
     //API doc says to return "null" for the us-east-1 region.
     if ("us-east-1".equals(regionString)) {
       gen.writeString("null");
+    } else {
+      gen.writeString(regionString);
     }
-    gen.writeString(regionString);
   }
 }

server/src/test/kotlin/com/adobe/testing/s3mock/dto/LocationConstraintTest.kt

@@ -30,4 +30,12 @@ internal class LocationConstraintTest {
     assertThat(iut).isNotNull()
     serializeAndAssert(iut, testInfo)
   }
+
+  @Test
+  @Throws(IOException::class)
+  fun testSerialization_usEastOne(testInfo: TestInfo) {
+    val iut = LocationConstraint(Region.fromValue("us-east-1"))
+    assertThat(iut).isNotNull()
+    serializeAndAssert(iut, testInfo)
+  }
 }

server/src/test/resources/com/adobe/testing/s3mock/dto/LocationConstraintTest_testSerialization_usEastOne.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+     Copyright 2017-2024 Adobe.
+
+     Licensed under the Apache License, Version 2.0 (the "License");
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+             http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+
+-->
+<LocationConstraint xmlns="http://s3.amazonaws.com/doc/2006-03-01/">null</LocationConstraint>