Grails 4: Null value in the configuration has been converted to empty String

[puneetbehl]

Task List

• Steps to reproduce provided
• Stacktrace (if present) provided
• Example that reproduces the problem uploaded to Github
• Full description of the issue provided (see below)

It looks like it's impossible to have a null value for a give configuration property in the application.yml as it is converted to an empty string. I think the problem is in YamlPropertySourceLoader.java which is responsible for loading properties from the YAML. It calls an underline spring method which flattens the input map and somehow converts a null value to an empty string.

Steps to Reproduce

1. Create a new Grails 4.0.3 application.
2. Define a property test: null in the application.yml
3. In the BootStrap.groovy add an assert to verify that the value is null as:

class BootStrap {

    def grailsApplication

    def init = { servletContext ->

        assert grailsApplication.config.test == null
        ...

Expected Behaviour

The value of the config property should be null.

Actual Behaviour

The assertion would fail as the value is an empty String.

Environment Information

• Operating System: macOS
• Grails Version: 4.0.3
• JDK Version: (AdoptOpenJDK)(build 1.8.0_232-b09)
• Container Version (If Applicable): N/A

Example Application

https://github.com/puneetbehl/grails-config-problem.git

[puneetbehl]

Relates to spring-projects/spring-framework#19986