Minor ticks don't work with tickformat %Y and ticklabelmode period

Minor ticks don't work as expected when the following three axis properties are combined:

  xaxis: {
    tickformat: '%Y',
    ticklabelmode: 'period',
    minor: {
      ticks: 'inside'
    }
  }

The minor ticks don't show up. Changing the tickformat to anything below the year frequency (e.g. %b %Y) lets the minor ticks appear. Removing the ticklabelmode also makes the minor ticks appear.

Here is a codepen that demonstrates the issue:
https://codepen.io/Djeramon/pen/vYQzPOa
Expected behaviour: Minor ticks should appear.

It is unclear, why the minor ticks shouldn't work with a yearly frequency on the major ticks.

从链接的 CodePen 复现开始，验证 yearly tickformat、ticklabelmode 'period' 和 minor ticks 之间的交互。跟踪坐标轴 tick 生成和标签模式的入口点，以确定为何会省略 minor ticks；当启用全部三个属性时 minor ticks 能够显示，并且现有用例仍能正常工作，即表示完成。