Minor code changes are the following:

-Removed unused variables from few files.
-Added null assertions in some tests.
-Added suppression of unused warning alongside the comments.
-Removed unnecessary throw exceptions.

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

@@ -71,15 +71,15 @@ class VisitController {
 		return visit;
 	}
 
-	// Spring MVC calls method loadPetWithVisit(...) before initNewVisitForm is
-	// called
+	@SuppressWarnings("unused") // Spring MVC calls method loadPetWithVisit(...) before
+	// initNewVisitForm is called
 	@GetMapping("/owners/{ownerId}/pets/{petId}/visits/new")
 	public String initNewVisitForm() {
 		return "pets/createOrUpdateVisitForm";
 	}
 
-	// Spring MVC calls method loadPetWithVisit(...) before processNewVisitForm is
-	// called
+	@SuppressWarnings("unused") // Spring MVC calls method loadPetWithVisit(...) before
+	// processNewVisitForm is called
 	@PostMapping("/owners/{ownerId}/pets/{petId}/visits/new")
 	public String processNewVisitForm(@ModelAttribute Owner owner, @PathVariable int petId, @Valid Visit visit,
 			BindingResult result, RedirectAttributes redirectAttributes) {

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

@@ -57,10 +57,6 @@ public class Vet extends Person {
 		return this.specialties;
 	}
 
-	protected void setSpecialtiesInternal(Set<Specialty> specialties) {
-		this.specialties = specialties;
-	}
-
 	@XmlElement
 	public List<Specialty> getSpecialties() {
 		List<Specialty> sortedSpecs = new ArrayList<>(getSpecialtiesInternal());

src/test/java/org/springframework/samples/petclinic/MySqlIntegrationTests.java

@@ -58,7 +58,7 @@ class MySqlIntegrationTests {
 	private RestTemplateBuilder builder;
 
 	@Test
-	void testFindAll() throws Exception {
+	void testFindAll() {
 		vets.findAll();
 		vets.findAll(); // served from cache
 	}

src/test/java/org/springframework/samples/petclinic/PetClinicIntegrationTests.java

@@ -44,7 +44,7 @@ public class PetClinicIntegrationTests {
 	private RestTemplateBuilder builder;
 
 	@Test
-	void testFindAll() throws Exception {
+	void testFindAll() {
 		vets.findAll();
 		vets.findAll(); // served from cache
 	}

src/test/java/org/springframework/samples/petclinic/PostgresIntegrationTests.java

@@ -17,6 +17,7 @@
 package org.springframework.samples.petclinic;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.fail;
 import static org.junit.jupiter.api.Assumptions.assumeTrue;
 
 import java.util.Arrays;
@@ -114,7 +115,20 @@ public class PostgresIntegrationTests {
 				Arrays.sort(names);
 				for (String name : names) {
 					String resolved = environment.getProperty(name);
-					String value = source.getProperty(name).toString();
+
+					if (resolved == null) {
+						fail("resolved property named {0} was expecting a string but is null.", name);
+						return;
+					}
+
+					Object sourceProperty = source.getProperty(name);
+
+					if (sourceProperty == null || sourceProperty.toString() == null) {
+						fail("source property named {0} was expecting a string value but is null.", name);
+						return;
+					}
+
+					String value = sourceProperty.toString();
 					if (resolved.equals(value)) {
 						log.info(name + "=" + resolved);
 					}

src/test/java/org/springframework/samples/petclinic/owner/PetTypeFormatterTests.java

@@ -68,7 +68,7 @@ class PetTypeFormatterTests {
 	}
 
 	@Test
-	void shouldThrowParseException() throws ParseException {
+	void shouldThrowParseException() {
 		given(this.pets.findPetTypes()).willReturn(makePetTypes());
 		Assertions.assertThrows(ParseException.class, () -> {
 			petTypeFormatter.parse("Fish", Locale.ENGLISH);

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

@@ -205,8 +205,6 @@ class ClinicServiceTests {
 		owner6.addVisit(pet7.getId(), visit);
 		this.owners.save(owner6);
 
-		owner6 = this.owners.findById(6);
-
 		assertThat(pet7.getVisits()) //
 			.hasSize(found + 1) //
 			.allMatch(value -> value.getId() != null);

src/test/java/org/springframework/samples/petclinic/system/CrashControllerTests.java

@@ -30,7 +30,7 @@ import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 // luck ((plain(st) UNIT test)! :)
 class CrashControllerTests {
 
-	CrashController testee = new CrashController();
+	final CrashController testee = new CrashController();
 
 	@Test
 	void testTriggerException() {

src/test/java/org/springframework/samples/petclinic/vet/VetTests.java

@@ -19,6 +19,7 @@ import org.junit.jupiter.api.Test;
 import org.springframework.util.SerializationUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.fail;
 
 /**
  * @author Dave Syer
@@ -33,6 +34,10 @@ class VetTests {
 		vet.setId(123);
 		@SuppressWarnings("deprecation")
 		Vet other = (Vet) SerializationUtils.deserialize(SerializationUtils.serialize(vet));
+		if (other == null) {
+			fail("other expected value but is null.");
+			return;
+		}
 		assertThat(other.getFirstName()).isEqualTo(vet.getFirstName());
 		assertThat(other.getLastName()).isEqualTo(vet.getLastName());
 		assertThat(other.getId()).isEqualTo(vet.getId());