In plumber2 your API can have multiple middleware that a request passes
through. At any point can you short-circuit the remaining middleware by
returning Break, which instructs plumber2 to return the response as is.
Returning Next indicates the opposite, ie that the request should be
allowed to pass on to the next middleware in the chain. A handler function
that doesn't return either of these are assumed to return a value that should
be set to the response body and implicitely continue to the next middleware.