Document params must be strings, numbers, or arrays of these (for repeated params) in programmatic navigation

[laurikihva]

Version

4.0.6

Reproduction link

https://codesandbox.io/s/dawn-pine-4yc98

Steps to reproduce

1. Press button on Home page which routes to About page with undefined id param.
2. Undefined id param is included in the URL & passed to About page as string

What is expected?

Undefined params are not passed to URL & on the redirected page this param value should also be undefined

What is actually happening?

Undefined is passed to the URL & is usable on the destination page as a string

---

Also happens if id is passed as null.

Doesn't matter if param is optional or not:

• path: "about/:id"
• path: "about/:id?

[posva]

Duplicate of #855

[posva]

Since this came up multiple times, I think we should say in the documentation that params must be strings