变量“接口”可能尚未初始化

Question

我试图建立一个Morphia和Spring应用程序中使用的模板从另一个项目，我收到以下错误

Variable 'assetRepository' might not have been initialized

这AssetRepository是一个接口

package code.nithin.repository;

import code.nithin.entity.Asset;

import org.mongodb.morphia.Key;

public interface AssetRepository {

    public Key<Asset> save(Asset asset);

}

并且AssetController是

package code.nithin.controllers;

import code.nithin.entity.Asset;

import code.nithin.repository.AssetRepository;

import org.mongodb.morphia.Key;

public class AssetController{

    public String saveAsset(String URL){

        AssetRepository assetRepository;

        Asset test = new Asset(1, System.currentTimeMillis(),"https://example.com");

        String returnString = assetRepository.save(test).getId();

    }

}

该实体是

package code.nithin.entity;

import org.bson.types.ObjectId;

import org.mongodb.morphia.annotations.Entity;

import org.mongodb.morphia.annotations.Id;

import lombok.Data;

import lombok.NoArgsConstructor;

@Data

@Entity("asset")

@NoArgsConstructor

public class Asset {

    @Id

    public ObjectId _id;

    public int version;

    public long timestamp;

    public String URL;

    public Asset(){}

    public Asset(int version, long timestamp, String URL) {

        this.version = version;

        this.timestamp = timestamp;

        this.URL = URL;

    }

    public ObjectId get_id() {

        return _id;

    }

    public void set_id(ObjectId _id) {

        this._id = _id;

    }

    public int getVersion() {

        return version;

    }

    public void setVersion(int version) {

        this.version = version;

    }

    public long getTimestamp() {

        return timestamp;

    }

    public void setTimestamp(long timestamp) {

        this.timestamp = timestamp;

    }

    public String getURL() {

        return URL;

    }

    public void setURL(String URL) {

        this.URL = URL;

    }

}

我所指的项目不会引发任何错误。