Waterline ORM does not populate related data

I can't get the Waterline ORM to hydrate my join. https://github.com/balderdashy/waterline-docs

I have the following two models:

// primary model

identity: 'document',
tableName: 'document',
attributes: {
    id: {
        type: 'integer',
        columnName: 'id',
        primaryKey: true,
        autoIncrement: true
    },

    // reference other models
    data: {
        model: 'document_data',
        columnName: 'id',
    },
},

// related model

identity: 'document_data',
tableName: 'document_data',
attributes: {
    documentId: {
        type: 'integer',
        columnName: 'document_id',
        primaryKey: true,
    },
    body: {
        type: 'text',
        columnName: 'body',
    },
},

I can see the following logged:

MySQL.processChildren: (SELECT * FROM document_data AS document_data WHERE document_id = 2 ORDER BY document_data.document_id ASC)

This is the correct query and I can confirm in the database. But the data key is not populated in the document model. It's just an empty object data: {}