Pipeline/Event/SourcePipelineEvent.php
public function addSource($source)
    {
        if (!is_array($source) && !($source instanceof \Traversable)) {
            throw new \InvalidArgumentException('source must be of type \Traversable|array');
        }

        $this->sources[] = $source;
    }
public function addSource($source)
    {
        if (!is_array($source) && !($source instanceof \Traversable)) {
            throw new \InvalidArgumentException('source must be of type \Traversable|array');
        }

        $this->sources[] = $source;
    }
@param \Traversable|array $source

@throws \InvalidArgumentException