PromptBuilder::validateMessages(): void

1375    private function validateMessages(): void1376    {1377        if (empty($this->messages)) {1378            throw new InvalidArgumentException('Cannot generate from an empty prompt. Add content using withText() or similar methods.');1379        }1380        $firstMessage = reset($this->messages);1381        if (!$firstMessage->getRole()->isUser()) {1382            throw new InvalidArgumentException('The first message must be from a user role, not from ' . $firstMessage->getRole()->value);1383        }1384        $lastMessage = end($this->messages);1385        if (!$lastMessage->getRole()->isUser()) {1386            throw new InvalidArgumentException('The last message must be from a user role, not from ' . $lastMessage->getRole()->value);1387        }1388        if (empty($lastMessage->getParts())) {1389            throw new InvalidArgumentException('The last message must have content parts. Add content using withText() or similar methods.');1390        }1391    }