lib/Parameters.php
public function requireParam($key)
    {
        $param = $this->fetch($key, function ($key) {
            throw new ParameterMissingException("Missing param '$key'");
        });

        if ($this->valueIsEmpty($param)) {
            throw new ParameterMissingException("Missing param '$key'");
        }

        return $param;
    }
public function requireParam($key)
    {
        $param = $this->fetch($key, function ($key) {
            throw new ParameterMissingException("Missing param '$key'");
        });

        if ($this->valueIsEmpty($param)) {
            throw new ParameterMissingException("Missing param '$key'");
        }

        return $param;
    }
Makes sure a parameter was passed

@param  string                    $key the parameter key
@return Parameters
@throws ParameterMissingException when parameter is missing