protected function addHelper( $data )
    {

        // array of values
        if( is_array( $data ) ) {

            $originalSize = count( $data );
            $data = array_filter( $data, '\Bond\is_not_null' );

            // have null
            if( $originalSize !== count( $data ) ) {
                $this->containsNull = true;
            }

            $argIntervals = array_map( null, $data, $data );
            $argIntervals = array_map( array($this, 'prepInterval'), $argIntervals );

            return array_filter( $argIntervals );

        } elseif( $data instanceof static ) {

            return $data->intervals;

        } elseif( $data === null ) {

            $this->containsNull = true;
            return array();

        } elseif( is_int($data) ) {

            return $this->parseStringToIntervals( $this->escape( $data ) );

        } elseif( is_scalar( $data ) ) {

            return $this->parseStringToIntervals( (string) $data );

        }

        throw new \RuntimeException( "Don't know how to handle this `{$data}`." );

    }