Add NullAway and JSpecify annotations

See gh-2016

Signed-off-by: Moritz Halbritter <moritz.halbritter@broadcom.com>

.github/workflows/gradle-build.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        java: [ '17' ]
+        java: [ '24' ]
 
     steps:
       - uses: actions/checkout@v4

.github/workflows/maven-build.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        java: [ '17' ]
+        java: [ '24' ]
 
     steps:
       - uses: actions/checkout@v4

.mvn/jvm.config

@@ -0,0 +1,10 @@
+--add-exports jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED
+--add-exports jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED
+--add-exports jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED
+--add-exports jdk.compiler/com.sun.tools.javac.model=ALL-UNNAMED
+--add-exports jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED
+--add-exports jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED
+--add-exports jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED
+--add-exports jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED
+--add-opens jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED
+--add-opens jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED

build.gradle

@@ -7,6 +7,7 @@ plugins {
   id 'org.cyclonedx.bom' version '3.0.0'
   id 'io.spring.javaformat' version '0.0.47'
   id "io.spring.nohttp" version "0.0.11"
+  id 'net.ltgt.errorprone' version '4.3.0'
 }
 
 gradle.startParameter.excludedTaskNames += [ "checkFormatAot", "checkFormatAotTest" ]
@@ -16,7 +17,7 @@ version = '4.0.0-SNAPSHOT'
 
 java {
   toolchain {
-    languageVersion = JavaLanguageVersion.of(17)
+    languageVersion = JavaLanguageVersion.of(24)
   }
 }
 
@@ -29,6 +30,8 @@ ext.springJavaformatCheckstyleVersion = "0.0.47"
 ext.webjarsLocatorLiteVersion = "1.1.1"
 ext.webjarsFontawesomeVersion = "4.7.0"
 ext.webjarsBootstrapVersion = "5.3.8"
+ext.errorProneVersion = "2.41.0"
+ext.nullAwayVersion = "0.12.9"
 
 dependencies {
   implementation 'org.springframework.boot:spring-boot-starter-cache'
@@ -55,6 +58,8 @@ dependencies {
   testImplementation 'org.testcontainers:mysql'
   checkstyle "io.spring.javaformat:spring-javaformat-checkstyle:${springJavaformatCheckstyleVersion}"
   checkstyle "com.puppycrawl.tools:checkstyle:${checkstyleVersion}"
+  errorprone "com.google.errorprone:error_prone_core:${errorProneVersion}"
+  errorprone "com.uber.nullaway:nullaway:${nullAwayVersion}"
 }
 
 tasks.named('test') {
@@ -71,6 +76,21 @@ checkstyleNohttp {
   configFile = file('src/checkstyle/nohttp-checkstyle.xml')
 }
 
+tasks.withType(JavaCompile).configureEach {
+  options.release = 17
+  options.errorprone {
+    disableAllChecks = true
+  }
+  if (name.equals("compileJava")) {
+    options.errorprone {
+      error("NullAway")
+      option("NullAway:OnlyNullMarked", "true")
+      option("NullAway:CustomContractAnnotations", "org.springframework.lang.Contract")
+      option("NullAway:JSpecifyMode", "true")
+    }
+  }
+}
+
 tasks.named("formatMain").configure { dependsOn("checkstyleMain") }
 tasks.named("formatMain").configure { dependsOn("checkstyleNohttp") }
 

pom.xml

@@ -18,7 +18,8 @@
   <properties>
 
     <!-- Generic properties -->
-    <java.version>17</java.version>
+    <java.version>24</java.version>
+    <maven.compiler.release>17</maven.compiler.release>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
     <!-- Important for reproducible builds. Update using e.g. ./mvnw versions:set -DnewVersion=... -->
@@ -37,6 +38,8 @@
     <nohttp-checkstyle.version>0.0.11</nohttp-checkstyle.version>
     <spring-format.version>0.0.47</spring-format.version>
 
+    <error-prone.version>2.41.0</error-prone.version>
+    <nullaway.version>0.12.9</nullaway.version>
   </properties>
 
   <dependencies>
@@ -275,6 +278,38 @@
           <failOnUnableToExtractRepoInfo>false</failOnUnableToExtractRepoInfo>
         </configuration>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <executions>
+          <execution>
+            <id>default-compile</id>
+            <phase>compile</phase>
+            <goals>
+              <goal>compile</goal>
+            </goals>
+            <configuration>
+              <compilerArgs>
+                <arg>-XDcompilePolicy=simple</arg>
+                <arg>--should-stop=ifError=FLOW</arg>
+                <arg>-Xplugin:ErrorProne -XepDisableAllChecks -Xep:NullAway:ERROR -XepOpt:NullAway:OnlyNullMarked=true -XepOpt:NullAway:CustomContractAnnotations=org.springframework.lang.Contract -XepOpt:NullAway:JSpecifyMode=true</arg>
+              </compilerArgs>
+              <annotationProcessorPaths>
+                <path>
+                  <groupId>com.google.errorprone</groupId>
+                  <artifactId>error_prone_core</artifactId>
+                  <version>${error-prone.version}</version>
+                </path>
+                <path>
+                  <groupId>com.uber.nullaway</groupId>
+                  <artifactId>nullaway</artifactId>
+                  <version>${nullaway.version}</version>
+                </path>
+              </annotationProcessorPaths>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
       <!-- Spring Boot Actuator displays sbom-related information if a CycloneDX SBOM file is
       present at the classpath -->
       <plugin>

src/main/java/org/springframework/samples/petclinic/PetClinicRuntimeHints.java

@@ -16,6 +16,8 @@
 
 package org.springframework.samples.petclinic;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.aot.hint.RuntimeHints;
 import org.springframework.aot.hint.RuntimeHintsRegistrar;
 import org.springframework.samples.petclinic.model.BaseEntity;
@@ -25,7 +27,7 @@ import org.springframework.samples.petclinic.vet.Vet;
 public class PetClinicRuntimeHints implements RuntimeHintsRegistrar {
 
 	@Override
-	public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
+	public void registerHints(RuntimeHints hints, @Nullable ClassLoader classLoader) {
 		hints.resources().registerPattern("db/*"); // https://github.com/spring-projects/spring-boot/issues/32654
 		hints.resources().registerPattern("messages/*");
 		hints.resources().registerPattern("mysql-default-conf");

src/main/java/org/springframework/samples/petclinic/model/BaseEntity.java

@@ -21,6 +21,7 @@ import jakarta.persistence.GeneratedValue;
 import jakarta.persistence.GenerationType;
 import jakarta.persistence.Id;
 import jakarta.persistence.MappedSuperclass;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Simple JavaBean domain object with an id property. Used as a base class for objects
@@ -34,13 +35,13 @@ public class BaseEntity implements Serializable {
 
 	@Id
 	@GeneratedValue(strategy = GenerationType.IDENTITY)
-	private Integer id;
+	private @Nullable Integer id;
 
-	public Integer getId() {
+	public @Nullable Integer getId() {
 		return id;
 	}
 
-	public void setId(Integer id) {
+	public void setId(@Nullable Integer id) {
 		this.id = id;
 	}
 

src/main/java/org/springframework/samples/petclinic/model/NamedEntity.java

@@ -18,6 +18,7 @@ package org.springframework.samples.petclinic.model;
 import jakarta.persistence.Column;
 import jakarta.persistence.MappedSuperclass;
 import jakarta.validation.constraints.NotBlank;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Simple JavaBean domain object adds a name property to <code>BaseEntity</code>. Used as
@@ -32,19 +33,20 @@ public class NamedEntity extends BaseEntity {
 
 	@Column(name = "name")
 	@NotBlank
-	private String name;
+	private @Nullable String name;
 
-	public String getName() {
+	public @Nullable String getName() {
 		return this.name;
 	}
 
-	public void setName(String name) {
+	public void setName(@Nullable String name) {
 		this.name = name;
 	}
 
 	@Override
 	public String toString() {
-		return this.getName();
+		String name = this.getName();
+		return (name != null) ? name : "<null>";
 	}
 
 }

src/main/java/org/springframework/samples/petclinic/model/Person.java

@@ -18,6 +18,7 @@ package org.springframework.samples.petclinic.model;
 import jakarta.persistence.Column;
 import jakarta.persistence.MappedSuperclass;
 import jakarta.validation.constraints.NotBlank;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Simple JavaBean domain object representing an person.
@@ -29,25 +30,25 @@ public class Person extends BaseEntity {
 
 	@Column(name = "first_name")
 	@NotBlank
-	private String firstName;
+	private @Nullable String firstName;
 
 	@Column(name = "last_name")
 	@NotBlank
-	private String lastName;
+	private @Nullable String lastName;
 
-	public String getFirstName() {
+	public @Nullable String getFirstName() {
 		return this.firstName;
 	}
 
-	public void setFirstName(String firstName) {
+	public void setFirstName(@Nullable String firstName) {
 		this.firstName = firstName;
 	}
 
-	public String getLastName() {
+	public @Nullable String getLastName() {
 		return this.lastName;
 	}
 
-	public void setLastName(String lastName) {
+	public void setLastName(@Nullable String lastName) {
 		this.lastName = lastName;
 	}
 

src/main/java/org/springframework/samples/petclinic/model/package-info.java

@@ -17,4 +17,7 @@
 /**
  * The classes in this package represent utilities used by the domain.
  */
+@NullMarked
 package org.springframework.samples.petclinic.model;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/org/springframework/samples/petclinic/owner/Owner.java

@@ -17,6 +17,7 @@ package org.springframework.samples.petclinic.owner;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Objects;
 
 import org.springframework.core.style.ToStringCreator;
 import org.springframework.samples.petclinic.model.Person;
@@ -32,6 +33,7 @@ import jakarta.persistence.OrderBy;
 import jakarta.persistence.Table;
 import jakarta.validation.constraints.Pattern;
 import jakarta.validation.constraints.NotBlank;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Simple JavaBean domain object representing an owner.
@@ -49,43 +51,43 @@ public class Owner extends Person {
 
 	@Column(name = "address")
 	@NotBlank
-	private String address;
+	private @Nullable String address;
 
 	@Column(name = "city")
 	@NotBlank
-	private String city;
+	private @Nullable String city;
 
 	@Column(name = "telephone")
 	@NotBlank
 	@Pattern(regexp = "\\d{10}", message = "{telephone.invalid}")
-	private String telephone;
+	private @Nullable String telephone;
 
 	@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
 	@JoinColumn(name = "owner_id")
 	@OrderBy("name")
 	private final List<Pet> pets = new ArrayList<>();
 
-	public String getAddress() {
+	public @Nullable String getAddress() {
 		return this.address;
 	}
 
-	public void setAddress(String address) {
+	public void setAddress(@Nullable String address) {
 		this.address = address;
 	}
 
-	public String getCity() {
+	public @Nullable String getCity() {
 		return this.city;
 	}
 
-	public void setCity(String city) {
+	public void setCity(@Nullable String city) {
 		this.city = city;
 	}
 
-	public String getTelephone() {
+	public @Nullable String getTelephone() {
 		return this.telephone;
 	}
 
-	public void setTelephone(String telephone) {
+	public void setTelephone(@Nullable String telephone) {
 		this.telephone = telephone;
 	}
 
@@ -104,7 +106,7 @@ public class Owner extends Person {
 	 * @param name to test
 	 * @return the Pet with the given name, or null if no such Pet exists for this Owner
 	 */
-	public Pet getPet(String name) {
+	public @Nullable Pet getPet(String name) {
 		return getPet(name, false);
 	}
 
@@ -113,11 +115,11 @@ public class Owner extends Person {
 	 * @param id to test
 	 * @return the Pet with the given id, or null if no such Pet exists for this Owner
 	 */
-	public Pet getPet(Integer id) {
+	public @Nullable Pet getPet(Integer id) {
 		for (Pet pet : getPets()) {
 			if (!pet.isNew()) {
 				Integer compId = pet.getId();
-				if (compId.equals(id)) {
+				if (Objects.equals(compId, id)) {
 					return pet;
 				}
 			}
@@ -131,7 +133,7 @@ public class Owner extends Person {
 	 * @param ignoreNew whether to ignore new pets (pets that are not saved yet)
 	 * @return the Pet with the given name, or null if no such Pet exists for this Owner
 	 */
-	public Pet getPet(String name, boolean ignoreNew) {
+	public @Nullable Pet getPet(String name, boolean ignoreNew) {
 		for (Pet pet : getPets()) {
 			String compName = pet.getName();
 			if (compName != null && compName.equalsIgnoreCase(name)) {

src/main/java/org/springframework/samples/petclinic/owner/OwnerController.java

@@ -16,6 +16,7 @@
 package org.springframework.samples.petclinic.owner;
 
 import java.util.List;
+import java.util.Objects;
 import java.util.Optional;
 
 import org.springframework.data.domain.Page;
@@ -34,6 +35,8 @@ import org.springframework.web.bind.annotation.RequestParam;
 import org.springframework.web.servlet.ModelAndView;
 
 import jakarta.validation.Valid;
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.web.servlet.mvc.support.RedirectAttributes;
 
 /**
@@ -60,7 +63,7 @@ class OwnerController {
 	}
 
 	@ModelAttribute("owner")
-	public Owner findOwner(@PathVariable(name = "ownerId", required = false) Integer ownerId) {
+	public Owner findOwner(@PathVariable(name = "ownerId", required = false) @Nullable Integer ownerId) {
 		return ownerId == null ? new Owner()
 				: this.owners.findById(ownerId)
 					.orElseThrow(() -> new IllegalArgumentException("Owner not found with id: " + ownerId
@@ -93,12 +96,13 @@ class OwnerController {
 	public String processFindForm(@RequestParam(defaultValue = "1") int page, Owner owner, BindingResult result,
 			Model model) {
 		// allow parameterless GET request for /owners to return all records
-		if (owner.getLastName() == null) {
+		String lastName = owner.getLastName();
-			owner.setLastName(""); // empty string signifies broadest possible search
+		if (lastName == null) {
+			lastName = ""; // empty string signifies broadest possible search
 		}
 
 		// find owners by last name
-		Page<Owner> ownersResults = findPaginatedForOwnersLastName(page, owner.getLastName());
+		Page<Owner> ownersResults = findPaginatedForOwnersLastName(page, lastName);
 		if (ownersResults.isEmpty()) {
 			// no owners found
 			result.rejectValue("lastName", "notFound", "not found");
@@ -143,7 +147,7 @@ class OwnerController {
 			return VIEWS_OWNER_CREATE_OR_UPDATE_FORM;
 		}
 
-		if (owner.getId() != ownerId) {
+		if (!Objects.equals(owner.getId(), ownerId)) {
 			result.rejectValue("id", "mismatch", "The owner ID in the form does not match the URL.");
 			redirectAttributes.addFlashAttribute("error", "Owner ID mismatch. Please try again.");
 			return "redirect:/owners/{ownerId}/edit";

src/main/java/org/springframework/samples/petclinic/owner/OwnerRepository.java

@@ -58,6 +58,6 @@ public interface OwnerRepository extends JpaRepository<Owner, Integer> {
 	 * @throws IllegalArgumentException if the id is null (assuming null is not a valid
 	 * input for id)
 	 */
-	Optional<Owner> findById(@Nonnull Integer id);
+	Optional<Owner> findById(Integer id);
 
 }

src/main/java/org/springframework/samples/petclinic/owner/Pet.java

@@ -32,6 +32,7 @@ import jakarta.persistence.ManyToOne;
 import jakarta.persistence.OneToMany;
 import jakarta.persistence.OrderBy;
 import jakarta.persistence.Table;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Simple business object representing a pet.
@@ -47,30 +48,30 @@ public class Pet extends NamedEntity {
 
 	@Column(name = "birth_date")
 	@DateTimeFormat(pattern = "yyyy-MM-dd")
-	private LocalDate birthDate;
+	private @Nullable LocalDate birthDate;
 
 	@ManyToOne
 	@JoinColumn(name = "type_id")
-	private PetType type;
+	private @Nullable PetType type;
 
 	@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
 	@JoinColumn(name = "pet_id")
 	@OrderBy("date ASC")
 	private final Set<Visit> visits = new LinkedHashSet<>();
 
-	public void setBirthDate(LocalDate birthDate) {
+	public void setBirthDate(@Nullable LocalDate birthDate) {
 		this.birthDate = birthDate;
 	}
 
-	public LocalDate getBirthDate() {
+	public @Nullable LocalDate getBirthDate() {
 		return this.birthDate;
 	}
 
-	public PetType getType() {
+	public @Nullable PetType getType() {
 		return this.type;
 	}
 
-	public void setType(PetType type) {
+	public void setType(@Nullable PetType type) {
 		this.type = type;
 	}
 

src/main/java/org/springframework/samples/petclinic/owner/PetController.java

@@ -17,10 +17,12 @@ package org.springframework.samples.petclinic.owner;
 
 import java.time.LocalDate;
 import java.util.Collection;
+import java.util.Objects;
 import java.util.Optional;
 
 import org.springframework.stereotype.Controller;
 import org.springframework.ui.ModelMap;
+import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 import org.springframework.validation.BindingResult;
 import org.springframework.web.bind.WebDataBinder;
@@ -32,6 +34,8 @@ import org.springframework.web.bind.annotation.PostMapping;
 import org.springframework.web.bind.annotation.RequestMapping;
 
 import jakarta.validation.Valid;
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.web.servlet.mvc.support.RedirectAttributes;
 
 /**
@@ -69,8 +73,8 @@ class PetController {
 	}
 
 	@ModelAttribute("pet")
-	public Pet findPet(@PathVariable("ownerId") int ownerId,
+	public @Nullable Pet findPet(@PathVariable("ownerId") int ownerId,
-			@PathVariable(name = "petId", required = false) Integer petId) {
+			@PathVariable(name = "petId", required = false) @Nullable Integer petId) {
 
 		if (petId == null) {
 			return new Pet();
@@ -135,7 +139,7 @@ class PetController {
 		// checking if the pet name already exists for the owner
 		if (StringUtils.hasText(petName)) {
 			Pet existingPet = owner.getPet(petName, false);
-			if (existingPet != null && !existingPet.getId().equals(pet.getId())) {
+			if (existingPet != null && !Objects.equals(existingPet.getId(), pet.getId())) {
 				result.rejectValue("name", "duplicate", "already exists");
 			}
 		}
@@ -160,7 +164,9 @@ class PetController {
 	 * @param pet The pet with updated details
 	 */
 	private void updatePetDetails(Owner owner, Pet pet) {
-		Pet existingPet = owner.getPet(pet.getId());
+		Integer id = pet.getId();
+		Assert.state(id != null, "'pet.getId()' must not be null");
+		Pet existingPet = owner.getPet(id);
 		if (existingPet != null) {
 			// Update existing pet's properties
 			existingPet.setName(pet.getName());

src/main/java/org/springframework/samples/petclinic/owner/PetTypeFormatter.java

@@ -21,6 +21,7 @@ import org.springframework.stereotype.Component;
 import java.text.ParseException;
 import java.util.Collection;
 import java.util.Locale;
+import java.util.Objects;
 
 /**
  * Instructs Spring MVC on how to parse and print elements of type 'PetType'. Starting
@@ -43,14 +44,15 @@ public class PetTypeFormatter implements Formatter<PetType> {
 
 	@Override
 	public String print(PetType petType, Locale locale) {
-		return petType.getName();
+		String name = petType.getName();
+		return (name != null) ? name : "<null>";
 	}
 
 	@Override
 	public PetType parse(String text, Locale locale) throws ParseException {
 		Collection<PetType> findPetTypes = this.types.findPetTypes();
 		for (PetType type : findPetTypes) {
-			if (type.getName().equals(text)) {
+			if (Objects.equals(type.getName(), text)) {
 				return type;
 			}
 		}

src/main/java/org/springframework/samples/petclinic/owner/Visit.java

@@ -24,6 +24,7 @@ import jakarta.persistence.Column;
 import jakarta.persistence.Entity;
 import jakarta.persistence.Table;
 import jakarta.validation.constraints.NotBlank;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Simple JavaBean domain object representing a visit.
@@ -37,10 +38,10 @@ public class Visit extends BaseEntity {
 
 	@Column(name = "visit_date")
 	@DateTimeFormat(pattern = "yyyy-MM-dd")
-	private LocalDate date;
+	private @Nullable LocalDate date;
 
 	@NotBlank
-	private String description;
+	private @Nullable String description;
 
 	/**
 	 * Creates a new instance of Visit for the current date
@@ -49,19 +50,19 @@ public class Visit extends BaseEntity {
 		this.date = LocalDate.now();
 	}
 
-	public LocalDate getDate() {
+	public @Nullable LocalDate getDate() {
 		return this.date;
 	}
 
-	public void setDate(LocalDate date) {
+	public void setDate(@Nullable LocalDate date) {
 		this.date = date;
 	}
 
-	public String getDescription() {
+	public @Nullable String getDescription() {
 		return this.description;
 	}
 
-	public void setDescription(String description) {
+	public void setDescription(@Nullable String description) {
 		this.description = description;
 	}
 

src/main/java/org/springframework/samples/petclinic/owner/VisitController.java

@@ -67,6 +67,10 @@ class VisitController {
 				"Owner not found with id: " + ownerId + ". Please ensure the ID is correct "));
 
 		Pet pet = owner.getPet(petId);
+		if (pet == null) {
+			throw new IllegalArgumentException(
+					"Pet with id " + petId + " not found for owner with id " + ownerId + ".");
+		}
 		model.put("pet", pet);
 		model.put("owner", owner);
 

src/main/java/org/springframework/samples/petclinic/owner/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package org.springframework.samples.petclinic.owner;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/org/springframework/samples/petclinic/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package org.springframework.samples.petclinic;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/org/springframework/samples/petclinic/system/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package org.springframework.samples.petclinic.system;
+
+import org.jspecify.annotations.NullMarked;

src/main/java/org/springframework/samples/petclinic/vet/Vet.java

@@ -31,6 +31,7 @@ import jakarta.persistence.JoinTable;
 import jakarta.persistence.ManyToMany;
 import jakarta.persistence.Table;
 import jakarta.xml.bind.annotation.XmlElement;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Simple JavaBean domain object representing a veterinarian.
@@ -47,7 +48,7 @@ public class Vet extends Person {
 	@ManyToMany(fetch = FetchType.EAGER)
 	@JoinTable(name = "vet_specialties", joinColumns = @JoinColumn(name = "vet_id"),
 			inverseJoinColumns = @JoinColumn(name = "specialty_id"))
-	private Set<Specialty> specialties;
+	private @Nullable Set<Specialty> specialties;
 
 	protected Set<Specialty> getSpecialtiesInternal() {
 		if (this.specialties == null) {

src/main/java/org/springframework/samples/petclinic/vet/Vets.java

@@ -20,6 +20,7 @@ import java.util.List;
 
 import jakarta.xml.bind.annotation.XmlElement;
 import jakarta.xml.bind.annotation.XmlRootElement;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Simple domain object representing a list of veterinarians. Mostly here to be used for
@@ -30,7 +31,7 @@ import jakarta.xml.bind.annotation.XmlRootElement;
 @XmlRootElement
 public class Vets {
 
-	private List<Vet> vets;
+	private @Nullable List<Vet> vets;
 
 	@XmlElement
 	public List<Vet> getVetList() {

src/main/java/org/springframework/samples/petclinic/vet/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package org.springframework.samples.petclinic.vet;
+
+import org.jspecify.annotations.NullMarked;

src/test/java/org/springframework/samples/petclinic/service/ClinicServiceTests.java

@@ -82,7 +82,7 @@ class ClinicServiceTests {
 	@Autowired
 	protected VetRepository vets;
 
-	Pageable pageable;
+	private final Pageable pageable = Pageable.unpaged();
 
 	@Test
 	void shouldFindOwnersByLastName() {

src/test/java/org/springframework/samples/petclinic/service/EntityUtils.java

@@ -43,7 +43,7 @@ public abstract class EntityUtils {
 	public static <T extends BaseEntity> T getById(Collection<T> entities, Class<T> entityClass, int entityId)
 			throws ObjectRetrievalFailureException {
 		for (T entity : entities) {
-			if (entity.getId() == entityId && entityClass.isInstance(entity)) {
+			if (entity.getId() != null && entity.getId() == entityId && entityClass.isInstance(entity)) {
 				return entity;
 			}
 		}