Flutter异常：在null上调用了getter'localPosition'

Question

使用this.fs = FileSystem.getLocal(conf);时遇到此异常：

NotificationListener

再现此错误所需的最少代码是：

════════ Exception caught by animation library ═════════════════════════════════
The getter 'localPosition' was called on null.
Receiver: null
Tried calling: localPosition
════════════════════════════════════════════════════════════════════════════════

要获取此异常，只需在iOS模拟器上滚动（变大）。

这是正常现象还是我做错了什么？