Though that is the common expression, it's probably more accurate to say:
If you do good things, pleasant things will happen to you;
If you do bad things, unpleasant things will happen to you.
Otherwise, if "good" leads to "good", then it can easily fall into a type of infinite progression. One single good thing would be enough to have an infinitely recurring amount of good things as results.
In the Dharma, deeds or actions, which are causes, are classified as wholesome, unwholesome, mixed or neutral (we could add "immovable", too); whereas experiences, which are results, are classified as pleasant, unpleasant, or neither nor.
It often helps to distinguish the two types of classification into the two types of action-causes and experience-results, respectively, to avoid confusion and the possibility of a doctrine entailing infinite repetition.
You could say there is no individual karma either because there is no individual to attribute kamma to.
But because we all perceive subject and object as distinct, it is sometimes more or less clear and necessary to discuss kamma in different modes of explanation.
Comforting a person facing recent suffering--> "Hey, stuff happens. It's not your or anyone's fault."
Counseling a person troubled by morality-->"Everything you do will have a result, everything until now has been because of your actions."
Kamma understood through meditation-->"There is no action and no result".
Even the idea of group kamma might be an applicable form of speech for a given situation. It may be good for a society's morality to be told that they are responsible as a group. For western individualists, this idea is absurd, but it can serve to bolster one's confidence to think of oneself as part of a responsible group than an individual who sinks and swims on their own.