Properly deal with dependencies for optional keys in the graph

[scizo]

An example:

(defnk component-a :- ComponentA
  [component-b :- ComponentB
   {component-c :- (s/maybe ComponentC) nil}]
  (->ComponentA component-b component-c))

I would expect that when a component-c key exists that it would be considered a dependency of component-a and started before start is called on component-a. This is currently not the case.

A work around does exist by building the graph with component/using

(def graph
  {:component-b fnk-that-builds-b
   :component-c fnk-that-builds-c
   :component-a (component/using fnk-that-builds-a {:component-c :component-c})})

It would be nice to not have to use component/using.