Using System Value for Base Currency Results in Config Error

[tsmith1985]

Checking Use system value for the base currency in the currency options results in a configuration error when importing currency rates.

Preconditions

• Magento CE v2.1.3
• PHP v7.0.14
• MySQL v14.14 Distrib 5.7.16, for osx 10.12

Steps to reproduce

1. Log into Admin
2. Navigate to Stores > Settings > Configuration > General > Currency Setup
3. Select Use system value for Base Currency
4. Select Yes for Enabled in the Scheduled Import Settings section
5. Click Save Config if necessary and flush the cache
6. Navigate to Stores > Currency > Currency Rates
7. Try Importing Currency Rates via any of the three services

Expected result

1. Currency rates are imported for Allowed Currencies

Actual result

1. You must first configure currency options before being able to see currency rates. is displayed on Currency Rates page and user is unable to import rates via any of the services.

Additional Notes

I was able to work around this issue by unselecting Use system value and explicitly selecting a Base Currency.

This issue seems to be a result of the base currency not being written to the database when Use system value is selected

mysql> mysql> select * from core_config_data where path='currency/options/base';
Empty set (0.00 sec) 

This results in this method failing to fetch the rates as $defaultCurrencies (actually base currencies) is empty:

<magento install dir>/vendor/magento/module-directory/Model/Currency/Import/AbstractImport.php#L92-L117

/**
  * @return array
  */
public function fetchRates()
{
    $data = [];
    $currencies = $this->_getCurrencyCodes();
    $defaultCurrencies = $this->_getDefaultCurrencyCodes();
    set_time_limit(0);
    foreach ($defaultCurrencies as $currencyFrom) {
        if (!isset($data[$currencyFrom])) {
            $data[$currencyFrom] = [];
        }
        foreach ($currencies as $currencyTo) {
            if ($currencyFrom == $currencyTo) {
                $data[$currencyFrom][$currencyTo] = $this->_numberFormat(1);
            } else {
                $data[$currencyFrom][$currencyTo] = $this->_numberFormat(
                    $this->_convert($currencyFrom, $currencyTo)
                );
            }
        }
        ksort($data[$currencyFrom]);
    }
    ini_restore('max_execution_time');
    return $data;
}

Also, the _getDefaultCurrencyCodes() method is getting the base currencies rather than the default currencies, which may be a bug or just a poor naming choice:

<magento install dir>/vendor/magento/module-directory/Model/Currency/Import/AbstractImport.php#L49-L52
protected function _getDefaultCurrencyCodes()
{
    return $this->_currencyFactory->create()->getConfigBaseCurrencies();
}

[veloraven]

@tsmith1985 thank you for your report.
We have created internal ticket MAGETWO-62921

[michael-tourneur]

@veloraven this issue has been fixed and merged?

[magento-engcom-team]

@tsmith1985, thank you for your report.
We've created internal ticket(s) MAGETWO-62921 to track progress on the issue.