I think there are two options to consider for this issue:

The first option is to leave the property in FlywayProperties as it is (@Nullable), simply remove .whenNot(List::isEmpty), and add tests to verify that when the property is not set, the default from Flyway is used.

The second option is to initialize ignoreMigrationPatterns field with a default value, remove .whenNot(List::isEmpty), and write tests to ensure that the default value is aligned with Flyway's default.

The second option is to initialize ignoreMigrationPatterns field with a default value, remove .whenNot(List::isEmpty), and write tests to ensure that the default value is aligned with Flyway's default.

This is the better approach. Where possible, it's good for the default value of a Boot property to match the default value of whatever Boot's configuring. That benefits property auto-completion in an IDE, for example. For IDEs that use the metadata (IntelliJ no longer does, AFAIK), we may need to add some manual metadata as I can't remember if the annotation processor understands Collections.singletonList, List.of or the like.

This is the better approach. Where possible, it's good for the default value of a Boot property to match the default value of whatever Boot's configuring.

In that case the test can verify ...containsExactly(new FluentConfiguration().getIgnoreMigrationPatterns()));

, we may need to add some manual metadata as I can't remember if the annotation processor understands Collections.singletonList, List.of or the like.

It does work for List<String> ignoreMigrationPatterns = Collections.singletonList("*:future");
but not for List<String> ignoreMigrationPatterns = new ArrayList<>(Collections.singletonList("*:future"));

I suggest add the following tests to cover all three scenarios:

@Test
void ignoreMigrationPatternsCorrectlyMapped() {
//"spring.flyway.ignore-migration-patterns=*:missing,*:future"
}

@Test
void ignoreMigrationPatternsWhenEmpty() {
//spring.flyway.ignore-migration-patterns=
}

@Test
void ignoreMigrationPatternsUsesDefaultValuesWhenNotSet() {
//when not set, should be aligned with Flyway's  new FluentConfiguration().getIgnoreMigrationPatterns()
}
	

P.S. Is it somehow possible to tell GitHub not to remove status: waiting-for-feedback?

P.S. Is it somehow possible to tell GitHub not to remove status: waiting-for-feedback?

Not at the moment: spring-io/issue-bot#23.

Thank you both, @wilkinsonaand @nosan, for the incredibly helpful and insightful discussion!

I've updated the PR with all the suggested changes. I really appreciate the detailed guidance on aligning the properties with Flyway's defaults and the correct way to test for it.

I've addressed it in ac59c8

Thanks @Chanwon-Seo !