`:multi` schema throws cryptic error when a string is used as a dispatch key

I'm trying to write multi schema to validate a map with strings as a key:

  (def valid?
    (m/validator
     [:multi {:dispatch "type"}
      ["object" [:map-of :keyword :string]]
      [::m/default :string]]))

Here is an exception thrown:

1. Caused by clojure.lang.ExceptionInfo
   :malli.core/sci-not-available
   {:type :malli.core/sci-not-available,
    :message :malli.core/sci-not-available,
    :data {:code "type"}}
                 core.cljc:  138  malli.core$_exception/invokeStatic
                 core.cljc:  136  malli.core$_exception/invoke
                 core.cljc:  142  malli.core$_fail_BANG_/invokeStatic
                 core.cljc:  140  malli.core$_fail_BANG_/invoke
                 core.cljc: 2346  malli.core$eval13299$_fail_BANG___13300/invoke
                 core.cljc: 2355  malli.core$eval13299$eval__13306/invoke
                 core.cljc: 1544  malli.core$_multi_schema$reify__12949/_into_schema
                 core.cljc: 1992  malli.core$into_schema/invokeStatic
                 core.cljc: 1983  malli.core$into_schema/invoke
                 core.cljc: 2052  malli.core$schema/invokeStatic
                 core.cljc: 2034  malli.core$schema/invoke
                 core.cljc: 2116  malli.core$validator/invokeStatic
                 core.cljc: 2110  malli.core$validator/invoke
                 core.cljc: 2114  malli.core$validator/invokeStatic
                 core.cljc: 2110  malli.core$validator/invoke
,,,

It looks like a string interpreted as an SCI expression, which is a bit surprising.

How about adding :dispatch-key property for :multi schema? This prop could be mutually exclusive with :dispatch but when present will be treated as a literal key to dispatch by. This allows to dispatch by any key, including string, var, object etc.