Tolerate jar files with no manifest in ChangeableUrls

Closes gh-5704

spring-boot-devtools/src/main/java/org/springframework/boot/devtools/restart/ChangeableUrls.java

@@ -119,10 +119,15 @@ final class ChangeableUrls implements Iterable<URL> {
 	}
 
 	private static List<URL> getUrlsFromClassPathAttribute(URL base, Manifest manifest) {
-		List<URL> urls = new ArrayList<URL>();
+		if (manifest == null) {
+			return Collections.<URL>emptyList();
+		}
 		String classPathAttribute = manifest.getMainAttributes()
 				.getValue(Attributes.Name.CLASS_PATH);
-		if (StringUtils.hasText(classPathAttribute)) {
+		if (!StringUtils.hasText(classPathAttribute)) {
+			return Collections.<URL>emptyList();
+		}
+		List<URL> urls = new ArrayList<URL>();
 		for (String entry : StringUtils.delimitedListToStringArray(classPathAttribute,
 				" ")) {
 			try {
@@ -133,7 +138,6 @@ final class ChangeableUrls implements Iterable<URL> {
 						"Class-Path attribute contains malformed URL", ex);
 			}
 		}
-		}
 		return urls;
 	}
 

spring-boot-devtools/src/test/java/org/springframework/boot/devtools/restart/ChangeableUrlsTests.java

@@ -24,6 +24,7 @@ import java.net.URLClassLoader;
 import java.util.jar.Attributes;
 import java.util.jar.JarOutputStream;
 import java.util.jar.Manifest;
+import java.util.zip.ZipOutputStream;
 
 import org.junit.Rule;
 import org.junit.Test;
@@ -80,7 +81,7 @@ public class ChangeableUrlsTests {
 		File relative = this.temporaryFolder.newFolder();
 		ChangeableUrls urls = ChangeableUrls.fromUrlClassLoader(new URLClassLoader(
 				new URL[] { makeJarFileWithUrlsInManifestClassPath(projectCore,
-						projectWeb, relative.getName() + "/") }));
+						projectWeb, relative.getName() + "/"), makeJarFileWithNoManifest() }));
 		assertThat(urls.toList(),
 				contains(projectCore, projectWeb, relative.toURI().toURL()));
 	}
@@ -105,4 +106,10 @@ public class ChangeableUrlsTests {
 		return classpathJar.toURI().toURL();
 	}
 
+	private URL makeJarFileWithNoManifest() throws Exception {
+		File classpathJar = this.temporaryFolder.newFile("no-manifest.jar");
+		new ZipOutputStream(new FileOutputStream(classpathJar)).close();
+		return classpathJar.toURI().toURL();
+	}
+
 }