Intermediate base class for read operations (GET, HEAD, List).
Note that definitions of
to success of operation itself, but do NOT
that content was found: it is possible for operation to succeed but
content not to be found (not to exist).
Server that successfully delivered content, if any
List of nodes that do not have entry for specified key.
Method called to indicate that the requested entry was missing from
specified server; will return either a new response object, or this
response modified with additional information.
server Server that was missing requested entry