Fix NPE in GzipResourceResolver

This change fixes a NullPointerException in GzipResourceResolver, which
assumed that calls to the `resolveResource` method were made with only
non-null values for request.

This is not the case for the VersionResourceResolver, which tries to
resolve resources that aren't requested per se by the HTTP request.

Issue: SPR-13149

spring-webmvc/src/main/java/org/springframework/web/servlet/resource/GzipResourceResolver.java

 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -48,7 +48,7 @@ public class GzipResourceResolver extends AbstractResourceResolver {
 			List<? extends Resource> locations, ResourceResolverChain chain) {
 
 		Resource resource = chain.resolveResource(request, requestPath, locations);
-		if ((resource == null) || !isGzipAccepted(request)) {
+		if ((resource == null) || (request != null && !isGzipAccepted(request))) {
 			return resource;
 		}
 

spring-webmvc/src/test/java/org/springframework/web/servlet/resource/GzipResourceResolverTests.java

@@ -149,4 +149,21 @@ public class GzipResourceResolverTests {
 		assertFalse("Expected " + resolved + " to *not* be of type " + EncodedResource.class,
 				resolved instanceof EncodedResource);
 	}
+
+	// SPR-13149
+	@Test
+	public void resolveWithNullRequest() throws IOException {
+
+		String file = "js/foo.js";
+		String gzFile = file+".gz";
+		Resource gzResource = new ClassPathResource("test/"+gzFile, getClass());
+
+		// resolved resource is now cached in CachingResourceResolver
+		Resource resolved = resolver.resolveResource(null, file, locations);
+
+		assertEquals(gzResource.getDescription(), resolved.getDescription());
+		assertEquals(new ClassPathResource("test/" + file).getFilename(), resolved.getFilename());
+		assertTrue("Expected " + resolved + " to be of type " + EncodedResource.class,
+				resolved instanceof EncodedResource);
+	}
 }