IntellijIdea违反了“合同条款'_-＆gt; null'”这是什么意思？

Question

我有一段代码：

public static Model parseModelObject(JSONObject objectJSON) {
    Project project = new Project();

    project.id = objectJSON.optInt(ID);
    project.title = objectJSON.optString(TITLE);
    project.idAuthor = objectJSON.optString(ID_AUTHOR);
    project.endDate = objectJSON.optString(END_DATE);
    project.aimAmount = objectJSON.optString(AIM_AMOUNT);
    project.currentAmount = objectJSON.optString(CURRENT_AMOUNT);
    project.createdAt = objectJSON.optString(_CREATED_AT);
    project.updatedAt = objectJSON.optString(_UPDATED_AT);
    project.status = objectJSON.optString(STATUS);
    project.description = objectJSON.optString(DESCRIPTION);
    project.logo = objectJSON.optString(LOGO);
    project.background = objectJSON.optString(BACKGROUND);
    return project;
}

并在线

 return project;

Intellij Idea出现警告：

  

合同条款'_-＆gt;违反了``

这是什么意思？