removeRelation(relation) {
    if (this._outgoingRelations) {
      const outgoingRelations = this.outgoingRelations;
      const i = outgoingRelations.indexOf(relation);
      if (i !== -1) {
        outgoingRelations.splice(i, 1);
      }
    }
    return this;
  }
Remove an outgoing Relation from the Asset by reference

@param  {Relation} relation Outgoing Relation
@return {Asset} The Asset itself