Add origin support for empty YAML list and map

[copa2]

While searching the root cause for spring-cloud/spring-cloud-config#1572 I reviewed OriginTrackedYamlLoader. In cases of an empty list or empty map there is no origin created.

Reproduction
Add to https://raw.githubusercontent.com/spring-projects/spring-boot/master/spring-boot-project/spring-boot/src/test/resources/org/springframework/boot/env/test-yaml.yml

emptylist: []
emptymap: {}

and extend testcases for emptylist and emptymap.

Fix
Add additional code for CollectionNodes which are empty In OriginTrackedYamlLoader.constructObject between ScalarNode and MappingNode check.

} else if (node instanceof CollectionNode && ((CollectionNode<?>) node).getValue().isEmpty()) {
   return constructTrackedObject(node, super.constructObject(node));
}

spring-boot/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/env/OriginTrackedYamlLoader.java

Lines 85 to 95 in a66c4d3

	protected Object constructObject(Node node) {
	if (node instanceof ScalarNode) {
	if (!(node instanceof KeyScalarNode)) {
	return constructTrackedObject(node, super.constructObject(node));
	}
	}
	else if (node instanceof MappingNode) {
	replaceMappingNodeKeys((MappingNode) node);
	}
	return super.constructObject(node);
	}

[mbhave]

Closing in favor of PR #21704.

[izeye]

It seems that @mbhave intended to close this.

[wilkinsona]

Thanks.