postgres: creation of custom fields

[mavuio]

Describe the bug
when creating a new custom field via a plugin the field cannot be created because
postgres complains when trying to create the fields

To Reproduce
❖ have at least one product in the products database
❖ create demo plugin:

import { VendurePlugin } from "@vendure/core";
export class DemoPlugin implements VendurePlugin {
  configure(config) {
    config.customFields.Product.push({
      type: "string",
      name: "dimensions"
    });
    return config;
  }
}

❖ yarn start
❖ see Error:

error 5/28/19, 10:27 AM - [TypeORM] Query error: error: column "customFieldsDimensions" contains null values, "ALTER TABLE "product" ADD "customFieldsDimensions" character varying NOT NULL" -- [undefined]
error 5/28/19, 10:27 AM - [TypeOrmModule] Unable to connect to the database. Retrying (2)... trace:
QueryFailedError: column "customFieldsDimensions" contains null values
    at new QueryFailedError (/Volumes/www/slideshop/src/error/QueryFailedError.ts:9:9)
    at Query.callback (/Volumes/www/slideshop/src/driver/postgres/PostgresQueryRunner.ts:176:30)
    at Query.handleError (/Volumes/www/slideshop/node_modules/pg/lib/query.js:142:17)
    at Connection.connectedErrorMessageHandler (/Volumes/www/slideshop/node_modules/pg/lib/client.js:194:17)
    at Connection.emit (events.js:182:13)
    at Connection.EventEmitter.emit (domain.js:442:20)
    at Socket.<anonymous> (/Volumes/www/slideshop/node_modules/pg/lib/connection.js:126:12)
    at Socket.emit (events.js:182:13)
    at Socket.EventEmitter.emit (domain.js:442:20)
    at addChunk (_stream_readable.js:283:12)

Expected behavior
no errors on creation

Environment (please complete the following information):

• @vendure/core version: 0.1.2-beta.2
• Nodejs version: 10.13.0
• Database (mysql/postgres etc): postgresql 11.3