Why?

(m/validate 
   [:map
    [:type :keyword]
    [:name {:min 1 :max 128} string?]]
   {:type :ledger :name ""}) => true

Try this:

(m/validate
  [:map
   [:type :keyword]
   [:name [:string {:min 1 :max 128}]]]
  {:type :ledger :name ""}) ;; false

(m/validate
  [:map
   [:type :keyword]
   [:name [:string {:min 1 :max 128}]]]
  {:type :ledger :name "foo"})  ;; true