GH-10083: Add Nullability to core support package

Related to:  #10083

* Add Nullability support to `support.management` package
* Add Nullability support to `support.management.micrometer` package
* Add Nullability support to  `support.management.observation`
* Add Nullability support to  `support.json`
* Removed nullable parameters from `fromJson`
* Disabled null checks in Deprecated Jackson2 classes
Remove Nullable from Jackson2 classes
* Remove Nullable from `AbstractLeaderEvent`
* Remove unnecessary `@SuppressWarnings`
* Remove unnecessary if statements following review

Author: cppwfs

spring-integration-core/src/main/java/org/springframework/integration/aggregator/DelegatingMessageGroupProcessor.java

@@ -47,6 +47,7 @@
  *
  *
  * @author Artem Bilan
+ * @author Glenn Renfro
  *
  * @since 5.2
  */
@@ -84,6 +85,7 @@ public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
 	@Override
 	public Object processMessageGroup(MessageGroup group) {
 		Object result = this.delegate.processMessageGroup(group);
+		Assert.state(result != null, "The delegate must return a non-null for the group");
 		if (!(result instanceof Message<?>) && !(result instanceof AbstractIntegrationMessageBuilder)) {
 			result = getMessageBuilderFactory()
 					.withPayload(result)

spring-integration-core/src/main/java/org/springframework/integration/json/JsonToObjectTransformer.java

@@ -180,7 +180,7 @@ protected Object doTransform(Message<?> message) {
 		catch (IOException e) {
 			throw new UncheckedIOException(e);
 		}
-
+		Assert.state(result != null, "Payload result must not be null");
 		if (removeHeaders) {
 			return getMessageBuilderFactory()
 					.withPayload(result)

spring-integration-core/src/main/java/org/springframework/integration/json/ObjectToJsonTransformer.java

@@ -22,6 +22,8 @@
 import java.io.UncheckedIOException;
 import java.util.Map;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.integration.support.json.JsonObjectMapper;
 import org.springframework.integration.support.json.JsonObjectMapperProvider;
 import org.springframework.integration.transformer.AbstractTransformer;
@@ -114,7 +116,7 @@ public String getComponentType() {
 	@Override
 	protected Object doTransform(Message<?> message) {
 		Object payload = buildJsonPayload(message.getPayload());
-
+		Assert.state(payload != null, "Payload result must not be null");
 		Map<String, Object> headers = new LinkedCaseInsensitiveMap<>();
 		headers.putAll(message.getHeaders());
 
@@ -136,7 +138,7 @@ else if (StringUtils.hasLength(this.contentType)) {
 				.build();
 	}
 
-	private Object buildJsonPayload(Object payload) {
+	private @Nullable Object buildJsonPayload(Object payload) {
 		try {
 			switch (this.resultType) {
 

spring-integration-core/src/main/java/org/springframework/integration/leader/event/AbstractLeaderEvent.java

@@ -16,8 +16,6 @@
 
 package org.springframework.integration.leader.event;
 
-import org.jspecify.annotations.Nullable;
-
 import org.springframework.context.ApplicationEvent;
 import org.springframework.integration.leader.Context;
 
@@ -32,18 +30,9 @@
 @SuppressWarnings("serial")
 public abstract class AbstractLeaderEvent extends ApplicationEvent {
 
-	private final @Nullable Context context;
-
-	private final @Nullable String role;
+	private final Context context;
 
-	/**
-	 * Create a new ApplicationEvent.
-	 *
-	 * @param source the component that published the event (never {@code null})
-	 */
-	public AbstractLeaderEvent(Object source) {
-		this(source, null, null);
-	}
+	private final String role;
 
 	/**
 	 * Create a new ApplicationEvent.
@@ -52,7 +41,7 @@ public AbstractLeaderEvent(Object source) {
 	 * @param context the context associated with this event
 	 * @param role the role of the leader
 	 */
-	public AbstractLeaderEvent(Object source, @Nullable Context context, @Nullable String role) {
+	public AbstractLeaderEvent(Object source, Context context, String role) {
 		super(source);
 		this.context = context;
 		this.role = role;
@@ -63,7 +52,7 @@ public AbstractLeaderEvent(Object source, @Nullable Context context, @Nullable S
 	 *
 	 * @return the context
 	 */
-	public @Nullable Context getContext() {
+	public Context getContext() {
 		return this.context;
 	}
 
@@ -72,7 +61,7 @@ public AbstractLeaderEvent(Object source, @Nullable Context context, @Nullable S
 	 *
 	 * @return the role
 	 */
-	public @Nullable String getRole() {
+	public String getRole() {
 		return this.role;
 	}
 

spring-integration-core/src/main/java/org/springframework/integration/splitter/AbstractMessageSplitter.java

@@ -234,7 +234,6 @@ else if (result instanceof Publisher<?> publisher) {
 		Map<String, Object> headers = messageHeaders;
 		Object correlationId = message.getHeaders().getId();
 		AtomicInteger sequenceNumber = new AtomicInteger(1);
-
 		return object -> createBuilder(object, headers, correlationId, sequenceNumber.getAndIncrement(), sequenceSize);
 	}
 
@@ -282,6 +281,7 @@ private AbstractIntegrationMessageBuilder<?> createBuilder(Object item, Map<Stri
 				.cloneMessageHistoryIfAny();
 
 		if (this.applySequence) {
+			Assert.state(correlationId != null, "Correlation ID must not be null.");
 			builder.pushSequenceDetails(correlationId, sequenceNumber, sequenceSize);
 		}
 

spring-integration-core/src/main/java/org/springframework/integration/support/BaseMessageBuilder.java

@@ -32,7 +32,6 @@
 import org.springframework.messaging.support.ErrorMessage;
 import org.springframework.messaging.support.GenericMessage;
 import org.springframework.util.Assert;
-import org.springframework.util.ObjectUtils;
 
 /**
  * The {@link AbstractIntegrationMessageBuilder} extension for the default logic to build message.
@@ -48,6 +47,7 @@
  * @param <B> the target builder class type.
  *
  * @author Artem Bilan
+ * @author Glenn Renfro
  *
  * @since 6.4
  *
@@ -63,12 +63,11 @@ public abstract class BaseMessageBuilder<T, B extends BaseMessageBuilder<T, B>>
 
 	private final IntegrationMessageHeaderAccessor headerAccessor;
 
-	@Nullable
-	private final Message<T> originalMessage;
+	private final @Nullable Message<T> originalMessage;
 
 	private volatile boolean modified;
 
-	private String[] readOnlyHeaders;
+	private String @Nullable [] readOnlyHeaders;
 
 	protected BaseMessageBuilder(T payload, @Nullable Message<T> originalMessage) {
 		Assert.notNull(payload, "payload must not be null");
@@ -285,7 +284,7 @@ public B setPriority(Integer priority) {
 	 * @return the current {@link BaseMessageBuilder}
 	 * @see IntegrationMessageHeaderAccessor#isReadOnly(String)
 	 */
-	public B readOnlyHeaders(@Nullable String... readOnlyHeaders) {
+	public B readOnlyHeaders(String @Nullable ... readOnlyHeaders) {
 		this.readOnlyHeaders = readOnlyHeaders != null ? Arrays.copyOf(readOnlyHeaders, readOnlyHeaders.length) : null;
 		if (readOnlyHeaders != null) {
 			this.headerAccessor.setReadOnlyHeaders(readOnlyHeaders);
@@ -317,7 +316,7 @@ public Message<T> build() {
 	}
 
 	private boolean containsReadOnly(MessageHeaders headers) {
-		if (!ObjectUtils.isEmpty(this.readOnlyHeaders)) {
+		if (this.readOnlyHeaders != null) {
 			for (String readOnly : this.readOnlyHeaders) {
 				if (headers.containsKey(readOnly)) {
 					return true;

spring-integration-core/src/main/java/org/springframework/integration/support/DefaultMessageBuilderFactory.java

@@ -25,13 +25,14 @@
 /**
  * @author Gary Russell
  * @author Artem Bilan
+ * @author Glenn Renfro
  *
  * @since 4.0
  *
  */
 public class DefaultMessageBuilderFactory implements MessageBuilderFactory {
 
-	private String[] readOnlyHeaders;
+	private String @Nullable [] readOnlyHeaders;
 
 	/**
 	 * Specify a list of headers which should be considered as a read only
@@ -41,7 +42,7 @@ public class DefaultMessageBuilderFactory implements MessageBuilderFactory {
 	 * and {@link org.springframework.messaging.MessageHeaders#TIMESTAMP}.
 	 * @since 4.3.2
 	 */
-	public void setReadOnlyHeaders(@Nullable String... readOnlyHeaders) {
+	public void setReadOnlyHeaders(String @Nullable ... readOnlyHeaders) {
 		this.readOnlyHeaders = readOnlyHeaders != null ? Arrays.copyOf(readOnlyHeaders, readOnlyHeaders.length) : null;
 	}
 
@@ -57,7 +58,7 @@ public void addReadOnlyHeaders(String... readOnlyHeaders) {
 		}
 		else {
 			headers = Arrays.copyOf(headers, headers.length + readOnlyHeaders.length);
-			System.arraycopy(readOnlyHeaders, 0, headers, this.readOnlyHeaders.length, readOnlyHeaders.length);
+			System.arraycopy(readOnlyHeaders, 0, headers, (this.readOnlyHeaders != null) ? this.readOnlyHeaders.length : 0, readOnlyHeaders.length);
 		}
 		this.readOnlyHeaders = headers;
 	}

spring-integration-core/src/main/java/org/springframework/integration/support/MutableMessageBuilder.java

@@ -45,6 +45,7 @@
  *
  * @author Gary Russell
  * @author Artem Bilan
+ * @author Glenn Renfro
  *
  * @since 4.0
  *
@@ -80,9 +81,8 @@ public Map<String, Object> getHeaders() {
 	}
 
 	@SuppressWarnings("unchecked")
-	@Nullable
 	@Override
-	public <V> V getHeader(String key, Class<V> type) {
+	public 	@Nullable <V> V getHeader(String key, Class<V> type) {
 		Object value = this.headers.get(key);
 		if (value == null) {
 			return null;
@@ -218,22 +218,22 @@ public AbstractIntegrationMessageBuilder<T> copyHeadersIfAbsent(@Nullable Map<St
 
 	@SuppressWarnings("unchecked")
 	@Override
-	protected List<List<Object>> getSequenceDetails() {
+	protected @Nullable List<List<Object>> getSequenceDetails() {
 		return (List<List<Object>>) this.headers.get(IntegrationMessageHeaderAccessor.SEQUENCE_DETAILS);
 	}
 
 	@Override
-	protected Object getCorrelationId() {
+	protected @Nullable Object getCorrelationId() {
 		return this.headers.get(IntegrationMessageHeaderAccessor.CORRELATION_ID);
 	}
 
 	@Override
-	protected Object getSequenceNumber() {
+	protected @Nullable Object getSequenceNumber() {
 		return this.headers.get(IntegrationMessageHeaderAccessor.SEQUENCE_NUMBER);
 	}
 
 	@Override
-	protected Object getSequenceSize() {
+	protected @Nullable Object getSequenceSize() {
 		return this.headers.get(IntegrationMessageHeaderAccessor.SEQUENCE_SIZE);
 	}
 

spring-integration-core/src/main/java/org/springframework/integration/support/NullAwarePayloadArgumentResolver.java

@@ -16,6 +16,8 @@
 
 package org.springframework.integration.support;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.messaging.converter.MessageConverter;
 import org.springframework.messaging.handler.annotation.support.PayloadMethodArgumentResolver;
 import org.springframework.validation.Validator;
@@ -40,7 +42,8 @@ public NullAwarePayloadArgumentResolver(MessageConverter messageConverter, Valid
 	}
 
 	@Override
-	protected boolean isEmptyPayload(Object payload) {
+	@SuppressWarnings("NullAway") // Dataflow analysis limitation
+	protected boolean isEmptyPayload(@Nullable Object payload) {
 		return super.isEmptyPayload(payload) || "KafkaNull".equals(payload.getClass().getSimpleName());
 	}
 

spring-integration-core/src/main/java/org/springframework/integration/support/PartialSuccessException.java

@@ -28,6 +28,7 @@
  *
  * @author Gary Russell
  * @author Artem Bilan
+ * @author Glenn Renfro
  *
  * @since 4.2
  *
@@ -97,7 +98,9 @@ public <T> Collection<T> getDerivedInput(Class<T> clazz) {
 
 	@Override
 	public String toString() {
-		return "PartialSuccessException [" + getMessage() + ":" + getCause().getMessage()
+		Throwable cause = getCause();
+		String causeMessage = (cause != null) ? cause.getMessage() : "";
+		return "PartialSuccessException [" + getMessage() + ":" + causeMessage
 				+ ", partialResults=" + this.partialResults + ", derivedInput=" + this.derivedInput
 				+ ", failedMessage=" + getFailedMessage() + "]";
 	}