Extend CollFold and IKVReduce to nil

Description

Currently, reduce-kv and fold throw when used on nil, because their respective protocols don't extend to nil. This seems strange, since Clojure tends to handle nils gracefully where possible, especially in places where collections are expected.

See thread https://groups.google.com/d/topic/clojure/tGI8sIKQoh0/discussion

Environment

None

Status

Assignee

Unassigned

Reporter

Herwig Hochleitner

Labels

None

Approval

Ok

Patch

Code and Test

Fix versions

Priority

Minor
Configure