Previously, in the absence of extensions of 'pipefs-service-type', we'd
get a wrong-type-arg exception while folding services:
In gnu/services/nfs.scm:
134:37 1 (_ #<<pipefs-configuration> mount-point: "/var/lib/nfs…> …)
In ice-9/boot-9.scm:
1685:16 0 (raise-exception _ #:continuable? _)
In procedure car: Wrong type argument in position 1 (expecting pair): ()
* gnu/services/nfs.scm (pipefs-service-type)[extend]: Gracefully handle
the case where VALUES is the empty list, as done in 'gss-service-type'.
7855a9366b