AxiosError.config can be undefined which is not reflected in types

[erksch]

Describe the bug

We encountered that the config property of AxiosError is undefined in some cases, we assume in the case of network errors. This is not reflected by the type of AxiosError.config which can lead to runtime issues and might crash your application if you try to read error.config.url for example.

To Reproduce

Create a network error where the request failed to send, retrieve error as an AxiosError and try to access one of the properties of error.config for example

error.config.url

Expected behavior

The type of AxiosError.config should say that it can be undefined.

Environment

• Axios Version 0.27.2
• Adapter: The one react native uses
• Node.js Version: v16.16.0
• OS: Linux, Ubuntu 22.04.
• Additional Library Versions: React 18.0, React Native 0.69.4

[Legion2]

possibly related to #4922, #4659 and #4711