Strange behavior with association ID if this ID in master table is null

[naveter]

MyBatis version

3.2.7

Database vendor and version

Postgresql 9.6.6, Oracle 12

There is a strange behavior with association ID if this ID in master table is null: MyBatis will set this association ID as ID of master table.

Test case or example project

Shema and data:

CREATE TABLE public.master (
  id SERIAL,
  slave_id INTEGER,
  CONSTRAINT master_pkey PRIMARY KEY(id)
);
INSERT INTO public.master (id, slave_id) VALUES (1, 2);
INSERT INTO public.master (id, slave_id) VALUES (2, 1);
INSERT INTO public.master (id, slave_id) VALUES (3, NULL);
CREATE TABLE public.slave (
  id SERIAL,
  name VARCHAR(100),
  CONSTRAINT slave_pkey PRIMARY KEY(id)
) 
INSERT INTO public.slave (id, name) VALUES (1, 'first');
INSERT INTO public.slave (id, name) VALUES (2, 'second');

mapper.xml:

<select id="selectMasters" resultMap="masterResultMap">
	select m.*, s.id as slaveid, s.name as name
	from public.master m
	left join public.slave s on s.id = m.slave_id
	order by m.id ASC
</select>

<resultMap id="slaveResult" type="learnspring.springmybatis.Slave" autoMapping="true">
	<result property="id" column="slaveid" />
	<result property="name" column="name" />
</resultMap>

<resultMap id="masterResultMap" type="learnspring.springmybatis.Master">
	<result property="id" column="id" />
	<result property="slave_id" column="slave_id" />
	<association property="slave" column="slave_id" resultMap="slaveResult"/>
</resultMap>

java:

List<Master> masters = session.selectList("learnspring.springmybatis.BlogMapper.selectMasters");
for (Master m : masters) {
	System.out.println(
		"master.id:" + m.getId()
		+ " master.slave_id:" + m.getSlave_id()
		+ " master.slave.id:" + (null != m.getSlave() ? m.getSlave().getId() : null)
		+ " master.slave.name:" + (null != m.getSlave() ? m.getSlave().getName() : null)
	);
}

Expected result

master.id:1 master.slave_id:2 master.slave.id:2 master.slave.name:second
master.id:2 master.slave_id:1 master.slave.id:1 master.slave.name:first
master.id:3 master.slave_id:null master.slave.id:null master.slave.name:null

Actual result

master.id:1 master.slave_id:2 master.slave.id:2 master.slave.name:second
master.id:2 master.slave_id:1 master.slave.id:1 master.slave.name:first
master.id:3 master.slave_id:null master.slave.id:3 master.slave.name:null

It can be cured by adding to association property 'notNullColumn':

<resultMap id="masterResultMap" type="learnspring.springmybatis.Master">
	<result property="id" column="id" />
	<result property="slave_id" column="slave_id" />
	<association property="slave" column="slave_id" resultMap="slaveResult" notNullColumn="slave_id"/>
</resultMap>

If do like that, MyBatis parses association correctly.
I do not know, there is a feature or bug, but I was very confused when saw such behavior in my work project.
Thanks a lot for yours work.

[harawata]

I think this is #895 which was fixed a while ago.
Let me know if it reproduces with the latest version (3.4.6 at this point).
Closing for now.