How to debug: "tags.0.1: Discarded invalid value"

I get this error on sentry.io:

40

I am using "@sentry/browser": "^5.4.3"
The tags I aim to set contains values like this:

version: '0.2.9',
revision: 'some-long-revision-guid',
branch: 'some-branch-name',

And I set the tags like this:

configureScope(scope => scope.setTag('version', version));

What is wrong - where can I see the invalid value?

From what it seems you are sending an empty string as tag, and we are discarding that.

Ok, I will try to implement a check for empty strings. But thats a weird error message :no_good_man: