Read empty string from JSON to empty List<...>

I have a List<String> field in my POJO. List so:

public class Student {
    private List<String> courseNames;
    ...
}

When the in-coming JSON (from 3rd-party) contains an array (like the following), it is not an issue.

{
    "courseNames": ["abc", "xyz"]
}

But the 3rd party app sometimes sends an empty array. Like so:

{
    "courseNames": ""
}

In this case, I like to have my courseNames field populated as an empty list.

Looking at this post, I figured implementing a custom JsonDeserializer is one way to achieve this.

So I partially implemented it:

public class StringToEmptyListJsonDeserializer extends JsonDeserializer<List<String>> {

    @Override
    public List<String> deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException, JacksonException {
        if(jsonParser.getCurrentToken() != JsonToken.START_ARRAY) {
            return new ArrayList<>();
        }
        return // What to do here?
    }
}

Are there any suggestions on how to delegate to the default List<...> JsonDeserializer? Or are there better solutions?

You can enable the DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT feature to allow JSON empty String value ("") to be bound as null for POJOs and other structured values (Maps, Collections). So the value will be converted either to a non empty list or an empty list like below:

@Data
public class Student {
    private List<String> courseNames;
}

ObjectMapper mapper = new ObjectMapper();
mapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);
//a non empty courseNames array 
String courseNames = "{\"courseNames\": [\"abc\", \"xyz\"]}";
Student student = mapper.readValue(courseNames, Student.class);
//ok, it prints {"courseNames":["abc","xyz"]}
System.out.println(mapper.writeValueAsString(student));
//an empty courseNames array
courseNames = "{\"courseNames\": []}";
student = mapper.readValue(courseNames, Student.class);
//ok, it prints the empty courseNames array
System.out.println(mapper.writeValueAsString(student));