Improve Javadoc for FileUtils.listFiles
This fixes
MODIFY
src/main/java/org/apache/commons/io/FileUtils.java
src/main/java/org/apache/commons/io/FileUtils.java
@@ -503,10 +503,11 @@ private static void innerListFiles(final Collection<File> files, final File dire
* in <code>FileFilterUtils.makeCVSAware(null)</code>.
*
* @param directory the directory to search in
- * @param fileFilter filter to apply when finding files.
+ * @param fileFilter filter to apply when finding files. Must not be {@code null},
+ * use {@link TrueFileFilter.INSTANCE} to match all files in selected directories.
* @param dirFilter optional filter to apply when finding subdirectories.
* If this parameter is {@code null}, subdirectories will not be included in the
- * search. Use TrueFileFilter.INSTANCE to match all directories.
+ * search. Use {@link TrueFileFilter.INSTANCE} to match all directories.
* @return a collection of java.io.File with the matching files
* @see org.apache.commons.io.filefilter.FileFilterUtils
* @see org.apache.commons.io.filefilter.NameFileFilter

IO-531 - Improve Javadoc for FileUtils.listFiles

This fixes #33