library/Rediska/Serializer/Adapter/Json.php
public function unserialize($value)
    {
        $decodedValue = json_decode($value);

        if ($decodedValue === null && $value !== 'null') {
            throw new Rediska_Serializer_Adapter_Exception("Can't unserialize value");
        }

        return $decodedValue;
    }
public function unserialize($value)
    {
        $decodedValue = json_decode($value);

        if ($decodedValue === null && $value !== 'null') {
            throw new Rediska_Serializer_Adapter_Exception("Can't unserialize value");
        }

        return $decodedValue;
    }
Unserialize value

@param mixed $value
@return string