static exists(lookupObj) {
        if (typeof this.session === "undefined") {
            throw new Error(
                [
                    `Tried to check if a ${this.modelName} model instance exists without a session. `,
                    "Create a session using `session = orm.session()` and call ",
                    `\`session["${this.modelName}"].exists\` instead.`,
                ].join("")
            );
        }

        return Boolean(this._findDatabaseRows(lookupObj).length);
    }
Returns a boolean indicating if an entity
with the given props exists in the state.

@param  {*}  props - a key-value that {@link Model} instances should have to be considered as existing.
@return {Boolean} a boolean indicating if entity with `props` exists in the state