If you set link to null, a new database connection is created. 如果将link设为null,就会创建一个新的数据库连接。
Next, specify a null because you're not adding a PDF link ( created with the AddLink method) target for this image. 下一步,指定一个空值,因为您没有为此图像添加PDF链接(通过AddLink方法创建)目标。
In the quiescent state, the next field of the link node pointed to by the tail is always null; in the intermediate state, it is always non-null. 在静止状态时,尾指针指向的链接节点的next字段总为null,而在中间状态时,这个字段为非null。
By default, the database settings type and link are set to null. 默认情况下,数据库配置type和link被设为null。