Create concave_hull by adding NULL values to the nearest concave_hull value

Question

I have a point layer with the "ID" field containing values from 1 to n, and some NULL values.

With the following expression, I manage to draw the concave_hull grouped by "ID" value:

concave_hull(collect(
             $geometry,
             group_by:=overlay_nearest(@layer,"ID",limit:=1))
             ,0.0)

Result:

I would like the NULL value to not create its own concave_hull. And instead of this, the points that have NULL value creates the concave_hull with the points of the nearest value. I try to explain what I am saying with an approximate representation of the expected result:

Answer 1

Use this expression:

concave_hull(
    collect(
        $geometry,
        group_by:=if (
            ID is NULL, 
            overlay_nearest (@layer, ID, filter:=ID is not NULL)[0],
            ID
        )
    )
    ,0
)

Points inside the blue circle have ID=NULL: