GH-10083: Nullability for graph in core module

* Add Nullability to core module's graph package.
* `buildGraph` and `getGraph` methods in the `IntegrationGraphServer` because Nullify could not see the creation of the graph
* `IntegrationGraphServer.receiptListRoutingHandler` required a change where the messageChannel could not be null in the `map` portion of expression.  So it was extracted into a var and the var was checked for null.

Author: cppwfs

spring-integration-core/src/main/java/org/springframework/integration/graph/CompositeMessageHandlerNode.java

@@ -19,6 +19,8 @@
 import java.util.ArrayList;
 import java.util.List;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.messaging.MessageHandler;
 
 /**
@@ -33,7 +35,7 @@ public class CompositeMessageHandlerNode extends MessageHandlerNode {
 
 	private final List<InnerHandler> handlers = new ArrayList<>();
 
-	public CompositeMessageHandlerNode(int nodeId, String name, MessageHandler handler, String input, String output,
+	public CompositeMessageHandlerNode(int nodeId, String name, MessageHandler handler, @Nullable String input, @Nullable String output,
 			List<InnerHandler> handlers) {
 
 		super(nodeId, name, handler, input, output);

spring-integration-core/src/main/java/org/springframework/integration/graph/DiscardingMessageHandlerNode.java

@@ -16,6 +16,8 @@
 
 package org.springframework.integration.graph;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.messaging.MessageHandler;
 
 /**
@@ -28,16 +30,16 @@
  */
 public class DiscardingMessageHandlerNode extends MessageHandlerNode {
 
-	private final String discards;
+	private final @Nullable String discards;
 
-	public DiscardingMessageHandlerNode(int nodeId, String name, MessageHandler handler, String input, String output,
-			String discards) {
+	public DiscardingMessageHandlerNode(int nodeId, String name, MessageHandler handler, @Nullable String input,
+			@Nullable String output, @Nullable String discards) {
 
 		super(nodeId, name, handler, input, output);
 		this.discards = discards;
 	}
 
-	public String getDiscards() {
+	public @Nullable String getDiscards() {
 		return this.discards;
 	}
 

spring-integration-core/src/main/java/org/springframework/integration/graph/EndpointNode.java

@@ -16,6 +16,8 @@
 
 package org.springframework.integration.graph;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * Base class for all endpoints.
  *
@@ -26,14 +28,14 @@
  */
 public abstract class EndpointNode extends IntegrationNode {
 
-	private final String output;
+	private final @Nullable String output;
 
-	protected EndpointNode(int nodeId, String name, Object nodeObject, String output) {
+	protected EndpointNode(int nodeId, String name, Object nodeObject, @Nullable String output) {
 		super(nodeId, name, nodeObject);
 		this.output = output;
 	}
 
-	public String getOutput() {
+	public @Nullable String getOutput() {
 		return this.output;
 	}
 

spring-integration-core/src/main/java/org/springframework/integration/graph/ErrorCapableCompositeMessageHandlerNode.java

@@ -18,6 +18,8 @@
 
 import java.util.List;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.integration.handler.CompositeMessageHandler;
 
 /**
@@ -31,17 +33,17 @@
  */
 public class ErrorCapableCompositeMessageHandlerNode extends CompositeMessageHandlerNode implements ErrorCapableNode {
 
-	private final String errors;
+	private final @Nullable String errors;
 
-	public ErrorCapableCompositeMessageHandlerNode(int nodeId, String name, CompositeMessageHandler handler, String input,
-			String output, String errors, List<InnerHandler> handlers) {
+	public ErrorCapableCompositeMessageHandlerNode(int nodeId, String name, CompositeMessageHandler handler,
+			@Nullable String input, @Nullable String output, @Nullable String errors, List<InnerHandler> handlers) {
 
 		super(nodeId, name, handler, input, output, handlers);
 		this.errors = errors;
 	}
 
 	@Override
-	public String getErrors() {
+	public @Nullable String getErrors() {
 		return this.errors;
 	}
 

spring-integration-core/src/main/java/org/springframework/integration/graph/ErrorCapableDiscardingMessageHandlerNode.java

@@ -16,6 +16,8 @@
 
 package org.springframework.integration.graph;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.messaging.MessageHandler;
 
 /**
@@ -29,17 +31,17 @@
  */
 public class ErrorCapableDiscardingMessageHandlerNode extends DiscardingMessageHandlerNode implements ErrorCapableNode {
 
-	private final String errors;
+	private final @Nullable String errors;
 
-	public ErrorCapableDiscardingMessageHandlerNode(int nodeId, String name, MessageHandler handler, String input,
-			String output, String discards, String errors) {
+	public ErrorCapableDiscardingMessageHandlerNode(int nodeId, String name, MessageHandler handler, @Nullable String input,
+			@Nullable String output, @Nullable String discards, @Nullable String errors) {
 
 		super(nodeId, name, handler, input, output, discards);
 		this.errors = errors;
 	}
 
 	@Override
-	public String getErrors() {
+	public @Nullable String getErrors() {
 		return this.errors;
 	}
 

spring-integration-core/src/main/java/org/springframework/integration/graph/ErrorCapableEndpointNode.java

@@ -16,6 +16,8 @@
 
 package org.springframework.integration.graph;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * Represents nodes that can natively handle errors.
  *
@@ -26,15 +28,15 @@
  */
 public class ErrorCapableEndpointNode extends EndpointNode implements ErrorCapableNode {
 
-	private final String errors;
+	private final @Nullable String errors;
 
-	protected ErrorCapableEndpointNode(int nodeId, String name, Object nodeObject, String output, String errors) {
+	protected ErrorCapableEndpointNode(int nodeId, String name, Object nodeObject, @Nullable String output, @Nullable String errors) {
 		super(nodeId, name, nodeObject, output);
 		this.errors = errors;
 	}
 
 	@Override
-	public String getErrors() {
+	public @Nullable String getErrors() {
 		return this.errors;
 	}
 

spring-integration-core/src/main/java/org/springframework/integration/graph/ErrorCapableMessageHandlerNode.java

@@ -16,6 +16,8 @@
 
 package org.springframework.integration.graph;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.messaging.MessageHandler;
 
 /**
@@ -27,17 +29,17 @@
  */
 public class ErrorCapableMessageHandlerNode extends MessageHandlerNode implements ErrorCapableNode {
 
-	private final String errors;
+	private final @Nullable String errors;
 
-	public ErrorCapableMessageHandlerNode(int nodeId, String name, MessageHandler handler, String input,
-			String output, String errors) {
+	public ErrorCapableMessageHandlerNode(int nodeId, String name, MessageHandler handler, @Nullable String input,
+			@Nullable String output, @Nullable String errors) {
 
 		super(nodeId, name, handler, input, output);
 		this.errors = errors;
 	}
 
 	@Override
-	public String getErrors() {
+	public @Nullable String getErrors() {
 		return this.errors;
 	}
 

spring-integration-core/src/main/java/org/springframework/integration/graph/ErrorCapableNode.java

@@ -16,6 +16,8 @@
 
 package org.springframework.integration.graph;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * Nodes implementing this interface are capable of emitting errors.
  *
@@ -26,6 +28,7 @@
  */
 public interface ErrorCapableNode {
 
+	@Nullable
 	String getErrors();
 
 }

spring-integration-core/src/main/java/org/springframework/integration/graph/ErrorCapableRoutingNode.java

@@ -18,6 +18,8 @@
 
 import java.util.Collection;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.messaging.MessageHandler;
 
 /**
@@ -31,17 +33,17 @@
  */
 public class ErrorCapableRoutingNode extends RoutingMessageHandlerNode implements ErrorCapableNode {
 
-	private final String errors;
+	private final @Nullable String errors;
 
-	public ErrorCapableRoutingNode(int nodeId, String name, MessageHandler handler, String input, String output,
-			String errors, Collection<String> routes) {
+	public ErrorCapableRoutingNode(int nodeId, String name, MessageHandler handler, @Nullable String input, @Nullable String output,
+			@Nullable String errors, Collection<String> routes) {
 
 		super(nodeId, name, handler, input, output, routes);
 		this.errors = errors;
 	}
 
 	@Override
-	public String getErrors() {
+	public @Nullable String getErrors() {
 		return this.errors;
 	}
 

spring-integration-core/src/main/java/org/springframework/integration/graph/IntegrationGraphRuntimeHints.java

@@ -16,6 +16,8 @@
 
 package org.springframework.integration.graph;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.aot.hint.BindingReflectionHintsRegistrar;
 import org.springframework.aot.hint.RuntimeHints;
 import org.springframework.aot.hint.RuntimeHintsRegistrar;
@@ -31,7 +33,7 @@
 class IntegrationGraphRuntimeHints implements RuntimeHintsRegistrar {
 
 	@Override
-	public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
+	public void registerHints(RuntimeHints hints, @Nullable ClassLoader classLoader) {
 		new BindingReflectionHintsRegistrar()
 				.registerReflectionHints(hints.reflection(),
 						Graph.class,