newFolder(String...) now throws IAE on an empty array

src/main/java/org/junit/rules/TemporaryFolder.java

@@ -182,9 +182,15 @@ public File newFolder(String path) throws IOException {
      * {@code "parent"} directory.
      */
     public File newFolder(String... paths) throws IOException {
-        // Before checking the paths, check if create() was ever called, and if it wasn't, throw
-        File root = getRoot();
+        if (paths.length == 0) {
+            throw new IllegalArgumentException("must pass at least one path");
+        }
 
+        /*
+         * Before checking if the paths are absolute paths, check if create() was ever called,
+         * and if it wasn't, throw IllegalStateException.
+         */
+        File root = getRoot();
         for (String path : paths) {
             if (new File(path).isAbsolute()) {
                 throw new IOException("folder path \'" + path + "\' is not a relative path");

src/test/java/org/junit/rules/TemporaryFolderUsageTest.java

@@ -141,6 +141,15 @@ public void newFolderWithGivenPathThrowsIllegalArgumentExceptionIfFolderExists()
         tempFolder.newFolder("level1", "level2", "level3");
     }
 
+    @Test
+    public void newFolderWithGivenEmptyArrayThrowsIllegalArgumentException() throws IOException {
+        tempFolder.create();
+
+        thrown.expect(IllegalArgumentException.class);
+        thrown.expectMessage("must pass at least one path");
+        tempFolder.newFolder(new String[0]);
+    }
+
     @Test
     public void newFolderWithPathsContainingForwardSlashCreatesFullPath()
             throws IOException {