Empty primitive extension

[Panthevm]

There are empty hash-maps in zen schemes

{ns hl7-fhir-r4-core.Element,
 import #{zen.fhir hl7-fhir-r4-core.string hl7-fhir-r4-core.Extension},
 schema
 {:zen/tags #{zen/schema zen.fhir/structure-schema},
  :zen/desc
  "Base StructureDefinition for Element Type: Base definition for all elements in a resource.",
  :zen.fhir/type "Element",
  :zen.fhir/profileUri
  "http://hl7.org/fhir/StructureDefinition/Element",
  :zen.fhir/version "0.5.16",
  :type zen/map,
  :keys
  {:id
   {:confirms #{hl7-fhir-r4-core.string/schema},
    :zen/desc "Unique id for inter-element referencing"},
    ;; ===============================
   :_id {},
   ;; ===============================
   :extension
   {:type zen/vector,
    :every
    {:confirms #{hl7-fhir-r4-core.Extension/schema},
     :zen/desc "Additional content defined by implementations"}}}}}