It is OK to call java.io.File.listFiles(FileFilter) with a null argument

See the Javadoc

Author: garydgregory

src/main/java/org/apache/commons/io/DirectoryWalker.java

@@ -644,7 +644,7 @@ private void walk(final File directory, final int depth, final Collection<T> res
             final int childDepth = depth + 1;
             if (depthLimit < 0 || childDepth <= depthLimit) {
                 checkIfCancelled(directory, depth, results);
-                File[] childFiles = filter == null ? directory.listFiles() : directory.listFiles(filter);
+                File[] childFiles = directory.listFiles(filter);
                 childFiles = filterDirectoryContents(directory, depth, childFiles);
                 if (childFiles == null) {
                     handleRestricted(directory, childDepth, results);

src/main/java/org/apache/commons/io/FileUtils.java

@@ -2306,7 +2306,7 @@ private static AccumulatorPathVisitor listAccumulate(final File directory, final
      */
     private static File[] listFiles(final File directory, final FileFilter fileFilter) throws IOException {
         requireDirectoryExists(directory, "directory");
-        final File[] files = fileFilter == null ? directory.listFiles() : directory.listFiles(fileFilter);
+        final File[] files = directory.listFiles(fileFilter);
         if (files == null) {
             // null if the directory does not denote a directory, or if an I/O error occurs.
             throw new IOException("Unknown I/O error listing contents of directory: " + directory);