docs: update filterExtensionsFromFileName method documentation to specify null parameter constraints

Author: Pfeil

src/main/java/edu/kit/datamanager/ro_crate/util/FileSystemUtil.java

@@ -20,9 +20,10 @@ private FileSystemUtil() {
      * Example:
      * filterExtensionsFromFileName("test.eln", Set.of("ELN")) -> "test"
      *
-     * @param filename the file name to filter
-     * @param extensionsToRemove the extensions to remove
+     * @param filename the file name to filter (must not be null)
+     * @param extensionsToRemove the extensions to remove (must not be null)
      * @return the filtered file name
+     * @throws NullPointerException if any parameter is null
      */
     public static String filterExtensionsFromFileName(String filename, Collection<String> extensionsToRemove) {
         String dot = Matcher.quoteReplacement(".");