Consistent not-null assertions for configured interceptors

Closes gh-25088

spring-messaging/src/main/java/org/springframework/messaging/support/AbstractMessageChannel.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -87,17 +87,20 @@ public abstract class AbstractMessageChannel implements MessageChannel, Intercep
 
 	@Override
 	public void setInterceptors(List<ChannelInterceptor> interceptors) {
+		Assert.noNullElements(interceptors, "'interceptors' must not contain null elements");
 		this.interceptors.clear();
 		this.interceptors.addAll(interceptors);
 	}
 
 	@Override
 	public void addInterceptor(ChannelInterceptor interceptor) {
+		Assert.notNull(interceptor, "'interceptor' must not be null");
 		this.interceptors.add(interceptor);
 	}
 
 	@Override
 	public void addInterceptor(int index, ChannelInterceptor interceptor) {
+		Assert.notNull(interceptor, "'interceptor' must not be null");
 		this.interceptors.add(index, interceptor);
 	}
 

spring-web/src/main/java/org/springframework/http/client/support/InterceptingHttpAccessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -24,6 +24,7 @@ import org.springframework.http.client.ClientHttpRequestFactory;
 import org.springframework.http.client.ClientHttpRequestInterceptor;
 import org.springframework.http.client.InterceptingClientHttpRequestFactory;
 import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
 import org.springframework.util.CollectionUtils;
 
 /**
@@ -57,6 +58,7 @@ public abstract class InterceptingHttpAccessor extends HttpAccessor {
 	 * @see AnnotationAwareOrderComparator
 	 */
 	public void setInterceptors(List<ClientHttpRequestInterceptor> interceptors) {
+		Assert.noNullElements(interceptors, "'interceptors' must not contain null elements");
 		// Take getInterceptors() List as-is when passed in here
 		if (this.interceptors != interceptors) {
 			this.interceptors.clear();