feat: accept single value as list

[WhiredPlanck]

(I connot run the test for "No JDK specified" exception, even I've specified, sorry)

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[WhiredPlanck]

I manage to run the tests, all yaml reading tests are passed.

@charleskorn Would you like to have a look?

[charleskorn]

Is there a reason why this needs to be implemented in Kaml rather than implemented as a custom serializer in your application?

[WhiredPlanck]

Is there a reason why this needs to be implemented in Kaml rather than implemented as a custom serializer in your application?

My original intention to do this is to implement the same feature as Jackson. There are many "single values" I need to accept them as list in the data I want to deserialize. Some data are cloned from upstreams and I connot control the format. And If I want to deserialize a field as Map<String, List<String>, things seem to be complex to do with a custom serializer.

UPDATE: YAML 1.2 specification does not allow it, but many parsers (such as Jackson) support it as a convenience feature that can be manually enabled or disabled for backward compatibility and usability, since YAML 1.1 specification allows this kind of implicit conversion.

[WhiredPlanck]

Is there a reason why this needs to be implemented in Kaml rather than implemented as a custom serializer in your application?

@charleskorn Recently I try to implement such kind a custom serializer and found that the (de)serialization will not (de)serailize the field with my custom serializer even I've specified it to the class or the field. I have no idea if it's a bug or I've made a mistake.