How do I add a global Gorm constraint to Grails 3 application.yml?

I want to add a global constraint to application.yml to make all fields in a domain class able to be null or blank. But I can't seem to get the syntax right. My domain class has about 30 fields and I want to avoid having to set constraints individually for every field. The examples on the Grails/Gorm site only show the old application.groovy syntax, below. I want to use application.yml instead:

grails.gorm.default.constraints = {
    '*'(nullable: true, size: 1..20)
}

I've tried variations of the following in application.yml, but get runtime exceptions when starting my Grails app.

grails:
    gorm:
      default:
        constraints:  '*' (nullable: true, blank: true)

Below is an example of the runtime exception:

Caused by: java.lang.RuntimeException: Cannot load application metadata: while parsing a block mapping
 in 'reader', line 137, column 9:
            constraints:  '*' nullable: true ... 
        ^
expected <block end>, but found Scalar in 'reader', line 137, column 27:
        constraints:  '*' nullable: true, blank: true

Does anyone have a good example of the syntax for application.yml?

Solution

Create application.groovy file in grails-app/conf/ and specify it there.