unknown_error, badarg when map function doesn't emit anything with a reduce function present but view called with reduce=false

• If a map function is in a case where it doesn't emit anything (conditional emit)
• If a reduce function is present (but not any built-in _count, _sum or _stats)
  Calling the view with reduce=false returns: {"error":"unknown_error","reason":"badarg"}

  expected:

  {"total_rows":0,"rows":[]}

Steps to reproduce:

Create a view with map function:
function (doc, meta) {
}

and reduce function:
function (key, values, rereduce)

Visit: http://localhost:8092/default/_design/dev_test/_view/empty?reduce=false&stale=false
(local install, design doc name is 'test', view name is 'empty')

Observe result: