try {
  const upsert = realm.create('ENTITY_NAME', obj,
	objects.length > 0 ? UpdateMode.Modified : UpdateMode.Never);
  console.log(`Upserted for entity: ${JSON.stringify(upsert)}`);
} catch (error) {
  console.error(`Failed to upsert for up entity ${JSON.stringify(obj)}: ${error.message}`);
}

const Realm = require('realm');

class Entity extends Realm.Object {
}

Entity.schema = {
  name: ENTITY_NAME,
  primaryKey: 'id',
  properties: {
    id: 'string',
    value: 'string',
    expiredTime: 'date',
    version: { type: 'int', default: 0 },
    schemaVersion: { type: 'int', default: 0 },
  },
};

export default Entity;

Realm object constructor must not return another value

class Entity {
}

"realm": "4.0.0-beta.0",
"react": "16.13.0",
"react-native": "0.61.5",
node v10.19.0
windows 10 64bit