lib/Promise/ReturnArgumentPromise.php
public function execute(array $args, FunctionProphecy $function)
    {
        return count($args) > $this->index ? $args[$this->index] : null;
    }
public function execute(array $args, FunctionProphecy $function)
    {
        return count($args) > $this->index ? $args[$this->index] : null;
    }
Returns nth argument if has one, null otherwise.

@param array          $args
@param FunctionProphecy $function

@return null|mixed