fixed so that nil is allowed as properties and empty properties are treated as nil (and stripped from m/form).

I don’t think nil should be treated as “always fail” in composite schemas. Currently, it will blow as nil is not a valid schema.

also, can’t strip all nils from children, as things like :enum might have actual valid value of nil.

So, options being: 1. allow (and strip) nil in map & composite schemas, for convenience sake 2. blow up in case of nil as child schema 3. map nil to “always fail”

the malli.util merge is not that fun for deeply nested maps:

(malli.util/merge 
  [:map [:x [:map [:y [:map [:z int?]] 
  (if require-z2 [:map [:x [:map [:y [:map [:z2 int?]]))

each into-schema should probably decide for itself what to do with nil values