public function call(array $params)
    {
        $this->initResolver();

        /**
         * makes sure that 'format' is passed and that 'API' and 'method'
         * parameters are not overwritten by defaults nor by call parameters
         */
        $defaults = array_merge(array('format' => $this->format), $this->defaultParams);
        $this->resolver->setDefaults($defaults);
        $this->resolver->setMandatory(array(
            'module' => 'API',
            'method' => $this->name()
        ));

        return $this->piwikClient->call($this->url(), $this->resolver->resolve($params));
    }