sails: Unique property throws error when using mongo

Waterline version:0.13.6 Node version:10.12.0 NPM version:6.4.1 Operating system:Ubuntu 18.10

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Related to - https://github.com/balderdashy/waterline/issues/1541, but no advice was given.

Currently trying to run the following code with sails-mongo. Have also tried with sails-disk and sails-memory and it is giving the same issue.

The following code results in the error: the attribute emailon theusermodel contains invalid properties. The propertyunique isn't a recognized property.

export const userCollection = Waterline.Collection.extend({
    identity: 'user',
    datastore: 'default',
    primaryKey: 'id',
    dontUseObjectIds: true,

    attributes: {
        id: {
            type: 'string',
            required: true
        },
        firstName: {type: 'string'},
        lastName: {type: 'string'},
        email: {type: 'string', required: true, unique: true}
        password: {type: 'string', required: true},

        roles: {
            collection: 'role'
        }
    }
}

const sailsMongoAdapter = require('sails-mongo');

export const datastoreConfig = {
    adapters: {
        'mongo': sailsMongoAdapter
    },

    datastores: {
        default: {
            adapter: 'mongo',
            url: 'mongodb://mongo:27017/db',
            schema:true
        }
    },
};

waterline.initialize(datastoreConfig, (err, ontology)=> {
    if (err) {
        console.error(err);
        throw err;
    }
}