Custom validator doesn't show message and is run twice.

Version: Vaadin 14.0.something (8 I think but I’m not very sure)

I’m binding a variable like this:

binder.forField(containers).withValidator(this::calculateValue, "One of the containers is invalid").bind("containers");

with a model that has a string called containers.
For some reason it doesn’t show an error message below the textfield when it’s wrong.
It also runs the validator twice for some reason. I don’t know why.
Later in the code I call:
Could it be that this overrides the previous one?