Leave field empty shows red line

I have a Blueprint that contains this:

blueprint:
  name: Example Blueprint
  description: This is an example
  domain: automation
  author: X
  input:
    my_test:
      name: Test
      description: This is an example
      default: ""

What I want is that this “my_test” field is optional. Now something strange is happening here.
When I click the field with my mouse, and then click another field, I get a red line. In my opinion that suggests that this field is required.

However, I can save the automation without any problems if I leave it empty, even when the red line is there. If I never click on the field, it will never get a red line.

In another scenario, where I did put a value in, and edit my automation later on, I can remove the value, and then the red line will never appear.

So… the field is optional in the end, but it appears otherwise… is this a bug?
I use HA 2023.4.6 container installation.