Hooks: explicit `undefined` values in `params`

[Cafe137]

For example, bee.uploadFile takes a name that is string | undefined.

When I pass undefined, I get that back in params, and have to filter out undefined entries as a workaround.

This may not be ideal, since a naive implementation to list all available params would cause wrong URLs:

http://localhost:1633/bzz?name=undefined

or

http://localhost:1633/pss/send/A/ffff?recipient=undefined