Menu has no children style error

[buildJava]

Describe the bug （描述 Bug）
When Menu has no children after change theme style error like

A clear and concise description of what the bug is.

To Reproduce （重现步骤）
Steps to reproduce the behavior:

set router without children and change theme then will see the menu which has no children does not show correct

cause

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior（你期待的是什么?）
A clear and concise description of what you expected to happen.
Thank you for the great component and fix this issue

Screenshots（截图）
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context（附加信息）
Add any other context about the problem here.

[buildJava]

also in light mode exist style issue,