Objectionjs: relation with multiple columns but some column could be null

Question

I have a Model, using Objection JS, with this relation:

class Model....{
...
static relationMappings = {
    ...
    evs:{
      relation: Model.ManyToManyRelation,
      modelClass: path.join(__dirname, 'evs-model'),
      join: {
        from: ['factura.factura_id', 'factura.uuid'],
        through: {
          from: ['_junction_evs.factura_id', '_junction_evs.uuid'],
          to: '_junction_evs.evidencia_id',
          extra: ['empresa_id', 'monto_pagado', 'monto_pesos']
        },
        to: 'evidencias_pagos.id',
      }
    }
  }
}

the problem is: when the column uuid is null (used in the "from" join), the await Model.relatedQuery('evs').for(id) returns empty array but I know is incorrect. How could I do this relation?