Prevent NullPointerException in AggregateReferenceDeserializerModifier.

In AggregateReferenceDeserializerModifier we now look up the original property name on the Jackson metadata before trying to resolve the property target type. We also explicitly guard against null values returned from that lookup and opt out of the customization in those cases.

spring-data-rest-webmvc/src/test/java/org/springframework/data/rest/webmvc/json/AggregateReferenceResolvingModuleUnitTests.java

@@ -0,0 +1,75 @@
+/*
+ * Copyright 2021 the original author or authors.
+ *
+ * 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
+ *
+ *      https://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.
+ */
+package org.springframework.data.rest.webmvc.json;
+
+import static org.assertj.core.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.springframework.data.keyvalue.core.mapping.context.KeyValueMappingContext;
+import org.springframework.data.mapping.context.PersistentEntities;
+import org.springframework.data.rest.core.UriToEntityConverter;
+import org.springframework.data.rest.core.annotation.RestResource;
+import org.springframework.data.rest.core.mapping.PersistentEntitiesResourceMappings;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+/**
+ * Unit tests for {@link AggregateReferenceResolvingModule}.
+ *
+ * @author Oliver Drotbohm
+ */
+@ExtendWith(MockitoExtension.class)
+public class AggregateReferenceResolvingModuleUnitTests {
+
+	@Mock UriToEntityConverter uriToEntityConverter;
+
+	@Test // GH-2033
+	void processesArtificialPropertiesCorrectly() {
+
+		KeyValueMappingContext<?, ?> context = new KeyValueMappingContext<>();
+		context.getPersistentEntity(Other.class);
+
+		PersistentEntities entities = PersistentEntities.of(context);
+		PersistentEntitiesResourceMappings mappings = new PersistentEntitiesResourceMappings(entities);
+
+		ObjectMapper mapper = new ObjectMapper()
+				.addMixIn(SomeType.class, SomeTypeMixin.class)
+				.registerModule(new AggregateReferenceResolvingModule(uriToEntityConverter, mappings));
+
+		assertThatNoException().isThrownBy(() -> {
+			mapper.readValue("{}", SomeType.class);
+		});
+	}
+
+	public static class SomeType {
+
+		public void setSomeProperty(Other other) {}
+	}
+
+	@RestResource
+	public static class Other {}
+
+	public abstract static class SomeTypeMixin {
+
+		// Rename property to expose a property that's not named like the actual member
+		@JsonProperty("foo")
+		public abstract void setSomeProperty(Other other);
+	}
+}