fix(params): enforce non-undefined route parameter values

- Update `Params` type to disallow `undefined` values for clarity.
- Default route parameter values to empty strings if `null` or `undefined`.

Signed-off-by: Max P. <Mail@MPassarello.de>

src/Types/Params.ts

@@ -7,4 +7,4 @@
  * All values are strings and should be considered read-only, as they are
  * extracted by the router and should not be modified by application code.
  */
-export type Params = Record<string, string | undefined>;
+export type Params = Record<string, string>;