Avoid a NPE if no password was given - use the default office one instead

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1494571 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/poi/poifs/crypt/Decryptor.java

@@ -96,6 +96,11 @@ public abstract class Decryptor {
 
     protected byte[] hashPassword(EncryptionInfo info,
                                   String password) throws NoSuchAlgorithmException {
+        // If no password was given, use the default
+        if (password == null) {
+            password = DEFAULT_PASSWORD;
+        }
+        
         MessageDigest sha1 = MessageDigest.getInstance("SHA-1");
         byte[] bytes;
         try {