+ // helper
+ public List<MetaData> filter(String source, String author, String tag) {
+ List<String> sources = source == null ? null : Arrays.asList(source);
+ List<String> authors = author == null ? null : Arrays.asList(author);
+ List<String> tags = tag == null ? null : Arrays.asList(tag);
+
+ return filter(sources, authors, tags);