New setting : return empty instance for an empty row (i.e. every column is NULL)

[harawata]

When a query returns a row with all columns being null (= an empty row), MyBatis returns null by default.
As per users' requests, a new configuration option returnInstanceForEmptyRow is added to change this behavior.
With this option enabled, MyBatis returns an empty instance instead of null for an empty row.

Note that this option also generates an empty instance for nested results (i.e. <collection /> and <association />) to meet a requirement like #420 .
To control this behavior individually, you may have to specify notNullColumn.

Please refer to the attached test cases for how it works and test your solutions with the latest 3.4.2-SNAPSHOT.

🔹 The existing option callSettersOnNulls is whether to call the property's setter method when the column value is null, so it has no effect on the above behavior. In version 3.2.x, it affected the returned value unintentionally.

[nlenoire]

Hello,

it looks like it is not possible to apply this settings using a constructor, but only an association or a collection element. Would it be possible to support it in constructor as well, to accommodate with immutable objects?

[dpawlak-pgs]

Look like it's not working for object created via constructor?