allow creating blank BIP32 by passing in null

lib/BIP32.js

@@ -10,6 +10,11 @@ var networks = require('../networks');
 var secp256k1_n = new bignum("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141", 16);
 var secp256k1_Gx = new bignum("79BE667EF9DCBBAC55A06295CE870B07029BFCDB2DCE28D959F2815B16F81798", 16);
 
+/*
+random new BIP32: new BIP32();
+from extended public or private key: new BIP32(str);
+new blank BIP32: new BIP32(null);
+*/
 var BIP32 = function(bytes) {
   if (typeof bytes == 'undefined' || bytes == 'mainnet' || bytes == 'livenet') {
     bytes = 'livenet';
@@ -46,7 +51,7 @@ var BIP32 = function(bytes) {
     }
   }
 
-  if (bytes !== undefined) 
+  if (bytes !== undefined && bytes !== null) 
     this.initFromBytes(bytes);
 }
 
@@ -60,7 +65,7 @@ BIP32.seed = function(bytes, network) {
     return false; //need more entropy
   var hash = coinUtil.sha512hmac(bytes, new Buffer("Bitcoin seed"));
 
-  var bip32 = new BIP32();
+  var bip32 = new BIP32(null);
   bip32.depth = 0x00;
   bip32.parentFingerprint = new Buffer([0, 0, 0, 0]);
   bip32.childIndex = new Buffer([0, 0, 0, 0]);
@@ -265,7 +270,7 @@ BIP32.prototype.deriveChild = function(i) {
     var priv = bignum.fromBuffer(this.eckey.private, {size: 32});
     var k = il.add(priv).mod(secp256k1_n);
 
-    ret = new BIP32();
+    ret = new BIP32(null);
     ret.chainCode = ir;
 
     ret.eckey = new Key();
@@ -289,7 +294,7 @@ BIP32.prototype.deriveChild = function(i) {
     var Kpar = Point.fromKey(oldkey);
     var newpub = Point.add(ilG, Kpar).toKey().public;
 
-    ret = new BIP32();
+    ret = new BIP32(null);
     ret.chainCode = new Buffer(ir);
 
     var eckey = new Key();