title: BelongsToMany eager loading returns multiple objects for each association
body: <p>I have two models: User and EconomicActivity. They are associated through UserEconomicActivity (it's a BelongsToMany relation). In User model, I have defined the association like this:</p>
  <pre class="lang-js prettyprint-override"><code>this.belongsToMany(models.EconomicActivity, {
    through: 'UserEconomicActivity',
    as: 'economicActivities',
    otherKey: {
      name: 'economicActivityId',
      allowNull: false
    },
    foreignKey: {
      name: 'userId',
      allowNull: false
    }
  })
  </code></pre>
  <p>I'm trying to query User where it is associated with one or more EconomicActivity, like this:</p>
  <pre class="lang-js prettyprint-override"><code>const users = await User.findAll({
    include: [
      {
        model: EconomicActivity,
        as: 'economicActivities',
        where: {
          id: filters.economicActivities // This is an array with IDs I want to filter
        }
      }
    ],
    raw: true,
    nest: true
  })
  </code></pre>
  <p>Let's say that one specific User is associated to 2 EconomicActivity. When I run this query, it returns the same user two times, one for each association. I want to return the same user just one time with an array of associated economicActivities inside it (like user.economicActivities). Is this possible?</p>