当我在lambda函数中使用new TypeReference<T>() {}并且T来自外部函数泛型参数时，它会抛出null异常。但是当这个语句直接写在函数中时就可以了。

• Java版本：8
• Jackson版本：2.12.5

有最小的可运行代码示例。
这将得到java.lang.IllegalArgumentException: Unrecognized Type: [null]

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.function.Function;

public class Main {

    public static void main(String[] args) {
        String test = "[\"test\"]";

        List<String> strings = getObjectConfig(test, new ArrayList<>());
        System.out.println(strings);
    }

    public static <T> T getObjectConfig(String key, T defaultValue) {
        return getCommon(
                key,
                v -> {
                    if (Objects.isNull(v)) {
                        return defaultValue;
                    } else {
                        try {
                            return new ObjectMapper().readValue(v, new TypeReference<T>() {});
                        } catch (JsonProcessingException e) {
                            throw new RuntimeException(e);
                        }
                    }
                }
        );
    }

    private static <T> T getCommon(String key, Function<String, T> transFunc) {
        try {
            String value = key;
            return transFunc.apply(value);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}

但这没关系。

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

import java.util.ArrayList;
import java.util.List;

public class Main {

    public static void main(String[] args) throws Exception {
        String test = "[\"test\"]";

        List<String> strings = getObjectConfig(test, new ArrayList<>());
        System.out.println(strings);
    }

    private static <T> T getObjectConfig(String key, T defaultValue) throws JsonProcessingException {
        return new ObjectMapper().readValue(key, new TypeReference<T>() {});
    }

}