public static function assert($value, $varName) {
        if(!is_array($value)) return Exceptions::InvalidTypeException('HashMapEntry', $varName, $value);
        if(count($value) > 1) return Exceptions::InvalidTypeException('HashMapEntry', $varName, $value);

        $keys = array_keys($value);
        $key  = end($keys);

        Str::assert($key, 'HashMapEntry of "' . $varName . '": "' . $key . '"');

        return $value;
    }