Adapt ViewResult for null and non-string keys.

Change-Id: If5cb3184860d57df2401a8537edf6d7259e38cec
Reviewed-on: http://review.couchbase.org/39157
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>