Using master. During startup, if you open `Window` -> `Console` and try and execute any command (can be garbage) `bitcoin-qt` will crash:
```bash
On branch pull/16118/local-merge

Process 89287 launched: '/Users/michael/github/bitcoin/src/qt/bitcoin-qt' (x86_64)
2019-05-29 09:57:56.276746-0400 bitcoin-qt[89287:939924] MessageTracer: Falling back to default whitelist
Process 89287 stopped
* thread #1, name = 'bitcoin-main', queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x8)
    frame #0: 0x00000001015158ba QtWidgets`QCompleter::popup() const + 10
QtWidgets`QCompleter::popup:
->  0x1015158ba <+10>: movq   0x8(%rdi), %rbx
    0x1015158be <+14>: movq   0x88(%rbx), %rax
    0x1015158c5 <+21>: testq  %rax, %rax
    0x1015158c8 <+24>: jne    0x101515942               ; <+146>
Target 0: (bitcoin-qt) stopped.
```

Not sure if just disabling the menu, like in #16118 would be ok, as a user might actually want to be able to run a command.
const int wallet_index = ui->WalletSelector->currentIndex();
        if (wallet_index > 0) {
            wallet_model = ui->WalletSelector->itemData(wallet_index).value<WalletModel*>();
        }
        if (m_last_wallet_model != wallet_model) {
            if (wallet_model) {
                message(CMD_REQUEST, tr("Executing command using \"%1\" wallet").arg(wallet_model->getWalletName()));
            } else {
                message(CMD_REQUEST, tr("Executing command without any wallet"));
            }
            m_last_wallet_model = wallet_model;
        }
#endif
        message(CMD_REQUEST, QString::fromStdString(strFilteredCmd));
        Q_EMIT cmdRequest(cmd, m_last_wallet_model);
        cmd = QString::fromStdString(strFilteredCmd);
        // R
        history.removeOne(cmd);
        // A
        history.append(cmd);
        // E
        while(history.size() > CONSOLE_HISTORY)
            history.removeFirst();
        // S
        historyPtr = history.size();
        // S
        scrollToEnd();
    }
}
void RPCConsole::browseHistory(int offset)