src/Application/SimpleApplication.php
public function pipeline(PipelineInterface $pipeline = null) : PipelineInterface
    {
        if ($pipeline){
            $this->pipeline = $pipeline;
        }
        if (!$this->pipeline){
            $this->pipeline = new NullPipeline;
        }
        return $this->pipeline;
    }
public function pipeline(PipelineInterface $pipeline = null) : PipelineInterface
    {
        if ($pipeline){
            $this->pipeline = $pipeline;
        }
        if (!$this->pipeline){
            $this->pipeline = new NullPipeline;
        }
        return $this->pipeline;
    }
Set/get pipeline

@param PipelineInterface $pipeline

@return PipelineInterface