Allow Cask refs

Library/Homebrew/cask/cask_loader.rb

@@ -52,12 +52,14 @@ module Cask
     # Loads a cask from a string.
     class FromContentLoader < AbstractContentLoader
       sig {
-        params(ref: T.any(Pathname, String, URI::Generic), warn: T::Boolean)
+        params(ref: T.any(Pathname, String, Cask, URI::Generic), warn: T::Boolean)
           .returns(T.nilable(T.attached_class))
       }
       def self.try_new(ref, warn: false)
-        return if ref.is_a?(URI::Generic)
-
+        case ref
+        when Cask, URI::Generic
+          # do nothing
+        else
           content = ref.to_str
 
           # Cache compiled regex
@@ -72,6 +74,7 @@ module Cask
 
           new(content)
         end
+      end
 
       sig { params(content: String, tap: Tap).void }
       def initialize(content, tap: T.unsafe(nil))