The null hypothesis would be to accept the state of things as they are. If there are very few women in computer science, you wouldn't assume it was due to some

The null hypothesis would be to accept the state of things as they are. If there are very few women in computer science, you wouldn't assume it was due to some conspiracy or "systematic discrimination" without any proof. You wouldn't enact policies of reverse discrimination (affirmative action) to correct some supposed imbalance of the system. You'd simply admit you don't know why, and search for proof of the reason.