Ignore fields with Optional.empty when performing Query by Example.

The Auditable interface introduces Optional getters, which when combined with Query by Example results in cryptic errors. By ignoring a probe's field that contains an Optional.empty, Query by Example works properly.

NOTE: This fix actually tests outside the originally detected scope of Auditable, verifying that ALL Optional.empty() fields are properly handled.

Closes spring-projects#2176
Original pull request spring-projects#2401

Author: gregturn

src/test/java/org/springframework/data/jpa/domain/sample/UserWithOptionalField.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2008-2022 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.jpa.domain.sample;
+
+import lombok.Data;
+
+import java.util.Optional;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.Id;
+
+import org.springframework.lang.Nullable;
+
+/**
+ * @author Greg Turnquist
+ */
+@Entity
+@Data
+public class UserWithOptionalField {
+
+	@Id @GeneratedValue private Long id;
+	private String name;
+	private String role;
+
+	public UserWithOptionalField() {
+
+		this.id = null;
+		this.name = null;
+		this.role = null;
+	}
+
+	public UserWithOptionalField(String name, @Nullable String role) {
+
+		this();
+		this.name = name;
+		this.role = role;
+	}
+
+	public Optional<String> getRole() {
+		return Optional.ofNullable(this.role);
+	}
+
+	public void setRole(Optional<String> role) {
+		this.role = role.orElse(null);
+	}
+}

src/test/java/org/springframework/data/jpa/domain/sample/UserWithOptionalFieldRepository.java

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2008-2022 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.jpa.domain.sample;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+
+/**
+ * @author Greg Turnquist
+ */
+public interface UserWithOptionalFieldRepository extends JpaRepository<UserWithOptionalField, Long> {}

src/test/java/org/springframework/data/jpa/domain/support/QueryByExampleWithOptionalEmptyTests.java

@@ -0,0 +1,73 @@
+/*
+ * Copyright 2008-2022 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.jpa.domain.support;
+
+import static org.assertj.core.api.Assertions.*;
+
+import java.util.List;
+import java.util.Optional;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.ImportResource;
+import org.springframework.data.domain.Example;
+import org.springframework.data.jpa.domain.sample.UserWithOptionalField;
+import org.springframework.data.jpa.domain.sample.UserWithOptionalFieldRepository;
+import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+/**
+ * Integration test for {@link org.springframework.data.repository.query.QueryByExampleExecutor} involving
+ * {@link Optional#empty()}.
+ *
+ * @author Greg Turnquist
+ */
+@ExtendWith(SpringExtension.class)
+@ContextConfiguration
+public class QueryByExampleWithOptionalEmptyTests {
+
+	@Autowired UserWithOptionalFieldRepository repository;
+	UserWithOptionalField user;
+
+	@Test
+	void queryByExampleTreatsEmptyOptionalsLikeNulls() {
+
+		// given
+		UserWithOptionalField user = new UserWithOptionalField();
+		user.setName("Greg");
+		repository.saveAndFlush(user);
+
+		// when
+		UserWithOptionalField probe = new UserWithOptionalField();
+		probe.setName("Greg");
+		Example<UserWithOptionalField> example = Example.of(probe);
+
+		// then
+		List<UserWithOptionalField> results = repository.findAll(example);
+
+		assertThat(results).hasSize(1);
+		assertThat(results).extracting(UserWithOptionalField::getName).containsExactly("Greg");
+	}
+
+	@Configuration
+	@EnableJpaRepositories(basePackageClasses = UserWithOptionalFieldRepository.class)
+	@ImportResource("classpath:infrastructure.xml")
+	static class JpaRepositoryConfig {}
+
+}