Polish WebJarsResourceResolver

Follow up to accb8519fd - same fix when resolving missing resources or
resolving a public URL for these resources.

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

@@ -63,7 +63,9 @@ public class WebJarsResourceResolver extends AbstractResourceResolver {
 		Resource resolved = chain.resolveResource(request, requestPath, locations);
 		if (resolved == null) {
 			String webJarResourcePath = findWebJarResourcePath(requestPath);
-			return chain.resolveResource(request, webJarResourcePath, locations);
+			if(webJarResourcePath != null) {
+				return chain.resolveResource(request, webJarResourcePath, locations);
+			}
 		}
 		return resolved;
 	}

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

@@ -99,7 +99,7 @@ public class WebJarsResourceResolverTests {
 	}
 
 	@Test
-	public void resolverUrlWebJarResourceNotFound() {
+	public void resolveUrlWebJarResourceNotFound() {
 		String file = "/something/something.js";
 		given(this.chain.resolveUrlPath(file, this.locations)).willReturn(null);
 
@@ -123,6 +123,18 @@ public class WebJarsResourceResolverTests {
 		verify(this.chain, times(1)).resolveResource(this.request, file, this.locations);
 	}
 
+	@Test
+	public void resolveResourceNotFound() {
+		String file = "/something/something.js";
+		given(this.chain.resolveUrlPath(file, this.locations)).willReturn(null);
+
+		Resource actual = this.resolver.resolveResource(this.request, file, this.locations, this.chain);
+
+		assertNull(actual);
+		verify(this.chain, times(1)).resolveResource(this.request, file, this.locations);
+		verify(this.chain, never()).resolveResource(this.request, null, this.locations);
+	}
+
 	@Test
 	public void resolveResourceWebJar() {
 		Resource expected = mock(Resource.class);