Well, if there are no statutes nor established case law precedents that apply to or can be extended to a particular situation, any cases would be more a matter of equity than law. And neither common law nor equity rulings apply a priori; a case must be brought to the court after the fact in order for the court to make a ruling on it. Common law also requires mens rea for any action to be considered an offense.
So even in a situation where a court would award damages if a case was filed and malicious or negligent harm were proved, I'm not really sure it makes sense to say that anything was "prohibited" in advance.
Not prohibited != can be done without legal consequence.
New torts are invented, albeit rarely. Every so often there's a new duty of care in negligence. There are, I'm sure, other examples and the point is this: the lack of case law wasn't much help to the first defendant to lose on that point.