Omit null properties from actuator endpoint API response examples

Closes gh-11757

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/endpoint/web/documentation/AbstractEndpointDocumentationTests.java

@@ -56,7 +56,8 @@ import static org.springframework.restdocs.payload.PayloadDocumentation.fieldWit
  * @author Andy Wilkinson
  */
 @TestPropertySource(properties = { "spring.jackson.serialization.indent_output=true",
-		"management.endpoints.web.expose=*" })
+		"management.endpoints.web.expose=*",
+		"spring.jackson.default-property-inclusion=non_null" })
 public class AbstractEndpointDocumentationTests {
 
 	protected String describeEnumValues(Class<? extends Enum<?>> enumType) {

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/endpoint/web/documentation/LiquibaseEndpointDocumentationTests.java

@@ -31,6 +31,7 @@ import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
 import org.springframework.restdocs.mockmvc.MockMvcRestDocumentation;
 import org.springframework.restdocs.payload.FieldDescriptor;
+import org.springframework.restdocs.payload.JsonFieldType;
 
 import static org.springframework.restdocs.payload.PayloadDocumentation.fieldWithPath;
 import static org.springframework.restdocs.payload.PayloadDocumentation.responseFields;
@@ -80,9 +81,11 @@ public class LiquibaseEndpointDocumentationTests
 				fieldWithPath("labels")
 						.description("Labels associated with the change set."),
 				fieldWithPath("checksum").description("Checksum of the change set."),
-				fieldWithPath("orderExecuted")
-						.description("Order of the execution of the change set."),
-				fieldWithPath("tag").description("Tag associated with the change set."));
+				fieldWithPath("orderExecuted").description(
+						"Order of the execution of the change set."),
+				fieldWithPath("tag")
+						.description("Tag associated with the change set, if any.")
+						.optional().type(JsonFieldType.STRING));
 	}
 
 	@Configuration

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/endpoint/web/documentation/MockMvcEndpointDocumentationTests.java

@@ -36,8 +36,7 @@ import org.springframework.web.context.WebApplicationContext;
  * @author Andy Wilkinson
  */
 @RunWith(SpringRunner.class)
-@SpringBootTest(properties = { "spring.jackson.serialization.indent_output=true",
-		"management.endpoints.web.expose=*" })
+@SpringBootTest
 public abstract class MockMvcEndpointDocumentationTests
 		extends AbstractEndpointDocumentationTests {
 

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/endpoint/web/documentation/ThreadDumpEndpointDocumentationTests.java

@@ -123,8 +123,8 @@ public class ThreadDumpEndpointDocumentationTests
 								fieldWithPath("threads.[].lockOwnerName")
 										.description("Name of the thread that owns the "
 												+ "object on which the thread is "
-												+ "blocked.")
-										.optional(),
+												+ "blocked, if any.")
+										.optional().type(JsonFieldType.STRING),
 								fieldWithPath("threads.[].priority")
 										.description("Priority of the thread. Only "
 												+ "available on Java 9 or later.")