message: improve unknown command error
diff: @@ -103,7 +103,9 @@ export class CommandNode {
  }
  _executeCommand(commandExecutor, options, targetOverride) {
  - if (this.isControlFlow()) {
  + if (!Commands.list.get(this.command.command)) {
  + throw new Error(`Unknown command ${this.command.command}`)
  + } else if (this.isControlFlow()) {
  return this._evaluate(commandExecutor)
  } else if (this.isTerminal()) {
  return Promise.resolve({
  