src/Message/AbstractRequest.php
public function validate()
    {
        foreach (func_get_args() as $key) {
            $value = $this->parameters->get($key);
            if (! isset($value)) {
                throw new InvalidRequestException("The $key parameter is required");
            }
        }
    }
public function validate()
    {
        foreach (func_get_args() as $key) {
            $value = $this->parameters->get($key);
            if (! isset($value)) {
                throw new InvalidRequestException("The $key parameter is required");
            }
        }
    }
Validate the request.

This method is called internally by gateways to avoid wasting time with an API call
when the request is clearly invalid.

@param string ... a variable length list of required parameters
@throws InvalidRequestException