Allow $set null (remove association)

[Antiavanti]

Referring to the documentation, use of null for relation $set() should be allowed.
https://sequelize.org/v5/manual/associations.html#associating-objects

// project is associated with task1 and task2
task2.setProject(null).then(() => {
  // and it's gone
})

[codecov]

Codecov Report

Merging #774 (1c7e980) into master (6b1e3ff) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #774   +/-   ##
=======================================
  Coverage   95.20%   95.20%           
=======================================
  Files         117      117           
  Lines        1126     1126           
  Branches      129      129           
=======================================
  Hits         1072     1072           
  Misses         22       22           
  Partials       32       32           

Impacted Files	Coverage Δ
src/model/model/model.ts	100.00% <ø> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6b1e3ff...1c7e980. Read the comment docs.

[engmsilva]

I'm not getting a way to remove an association between these two models below:

@Table
class Ticket extends Model {
  @PrimaryKey
  @AutoIncrement
  @Column
  id: number;

  @ForeignKey(() => Queue)
  @Column
  queueId: number;

  @BelongsTo(() => Queue)
  queue: Queue;
  
}

@Table
class Queue extends Model {
  @PrimaryKey
  @AutoIncrement
  @Column
  id: number;
}

To associate a Queue to a Ticket I do the following:

const queueId = 1;
await Ticket.findByPk(ticket.id).then(async ticket => {
          await ticket.update({
            queueId
          });
ticket.reload();
  });

Any ideas on how to remove this association?