account_update2 validation fails requiring optional parameters

Hello,

With hf21, it's now possible to update your json_metadata without the active key (https://github.com/steemit/steem/releases/tag/v0.21.0) thanks to the operation account_update2

 struct account_update2_operation : public base_operation
{
   account_name_type             account;
   optional< authority >         owner;
   optional< authority >         active;
   optional< authority >         posting;
   optional< public_key_type >   memo_key;
   string                        json_metadata;
   string                        posting_json_metadata;

   extensions_type               extensions;
};

The parameters are very close to account_update but the keys are optional.

Expected behavior

I can update my account with my posting keys

Actual behavior

The validation requires a memo key, (which is optional), which makes the whole thing fail. And if the memo key is added then the operation requires the active key which defeats the purpose of account_update2

How to reproduce

var steem = require('steem');
steem.api.setOptions({url: 'https://testnet.steemitdev.com/', useAppbaseApi :  true, address_prefix : 'TST', 'chain_id' : "46d82ab7d8db682eb1959aed0ada039a6d49afa1602491f93dde9cac3e8e6c32"});
steem.config.set('address_prefix', 'TST')
steem.config.set('chain_id', '46d82ab7d8db682eb1959aed0ada039a6d49afa1602491f93dde9cac3e8e6c32')


async function account_update() {
    
    const username = "howo";
    const wif = "mysupersecretpostingkey";
    
    let ops = [];


    let account = await steem.api.callAsync('condenser_api.get_accounts', [[username]]);
    account = account[0];


    ops.push(['account_update2', {
        'account': username,
        posting_key: account.posting.key_auths[0][0],
        active_key: account.active.key_auths[0][0],
        owner_key: account.owner.key_auths[0][0],
        'json_metadata': "",
        "posting_json_metadata": ""
    }]);


    let tx = {operations: ops, extensions: []};
    
    steem.broadcast.send(tx, {posting: wif}, async function (err) {
        if (!err) {
            console.log("yey")
        } else {
            console.log(":'(");
            console.log(err);
        }
    });
}

Environment information

steem: 0.7.6, node 10.6

I believe the problem is with this line:

steem-js/src/auth/serializer/src/operations.js

Line 615 in 42f1382

memo_key: public_key,

It should read:

memo_key: optional(public_key),

Yep, I've tested locally and that was the issue. Thanks @mvandeberg