getProperty (path) {
    if (path.length !== 2) {
      throw new Error('path must have length=2')
    }
    const [nodeId, propName] = path
    const node = this.get(nodeId)
    if (node) {
      return node.getSchema().getProperty(propName)
    } else {
      throw new Error('Invalid path.')
    }
  }
Retrieve the NodeProperty for a given path

@param {string[]} path