Add test for FunctionAroundWrapper

spring-cloud-function-context/src/main/java/org/springframework/cloud/function/context/catalog/SimpleFunctionRegistry.java

@@ -188,7 +188,9 @@ public class SimpleFunctionRegistry implements FunctionRegistry, FunctionInspect
 			logger.debug("Function '" + functionDefinition + "' is not found in cache");
 		}
 
-		function = this.wrapInAroundAviceIfNecessary(function);
+		if (function != null) {
+			function = this.wrapInAroundAviceIfNecessary(function);
+		}
 
 		return (T) function;
 	}

spring-cloud-function-context/src/test/java/org/springframework/cloud/function/context/catalog/MarcinSleuthTests.java

@@ -0,0 +1,86 @@
+/*
+ * Copyright 2021-2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.function.context.catalog;
+
+import java.util.function.Function;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.builder.SpringApplicationBuilder;
+import org.springframework.cloud.function.context.FunctionCatalog;
+import org.springframework.cloud.function.context.catalog.SimpleFunctionRegistry.FunctionInvocationWrapper;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.support.MessageBuilder;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Oleg Zhurakousky
+ */
+public class MarcinSleuthTests {
+
+	private ApplicationContext context;
+
+	private FunctionCatalog configureCatalog(Class<?>... configClass) {
+		this.context = new SpringApplicationBuilder(configClass)
+				.run("--logging.level.org.springframework.cloud.function=DEBUG",
+						"--spring.main.lazy-initialization=true");
+		FunctionCatalog catalog = context.getBean(FunctionCatalog.class);
+		return catalog;
+	}
+
+	@BeforeEach
+	public void before() {
+		System.clearProperty("spring.cloud.function.definition");
+	}
+
+	@Test
+	public void testMarcinHeaderInjection() {
+		FunctionCatalog catalog = this.configureCatalog(SampleFunctionConfiguration.class);
+
+		FunctionInvocationWrapper function = catalog.lookup("echo", "application/json");
+		Message<byte[]>  result = (Message<byte[]>) function.apply(MessageBuilder.withPayload("hello").build());
+		assertThat(result.getHeaders().get("his-name")).isEqualTo("marcin");
+	}
+
+	@EnableAutoConfiguration
+	@Configuration
+	protected static class SampleFunctionConfiguration {
+
+		@Bean
+		public Function<Message<String>, Message<String>> echo() {
+			return m -> m;
+		}
+
+		@Bean
+		public FunctionAroundWrapper aroundWrapper() {
+			return new FunctionAroundWrapper() {
+
+				@Override
+				protected Object doApply(Message<byte[]> input,
+						FunctionInvocationWrapper targetFunction) {
+					return targetFunction.apply(MessageBuilder.fromMessage(input).setHeader("his-name", "marcin").build());
+				}
+			};
+		}
+	}
+}