Type error when fallback option with undefined.

[taku-hatano]

Bug report

Description / Observed Behavior

An error will occur if the fallback option for useSWR is undefined.

const { data, error } = useSWR("/api/hello", {
  fallback: undefined
});

fallback option can be specified as undefined in the type definition.　　
The above code causes the following error.

TypeError: Cannot read properties of undefined (reading '/api/hello')

Expected Behavior

I think fallback option should check if it is undefined.
(For example, here)

Repro Steps / Code Example

CodeSandbox

Additional Context

SWR version. 2.2.5
Add any other context about the problem here.