Ensure IndifferentAccess is injected after merge

During non-destructive merges (i.e. `#merge`), the `IndifferentAccess` mixin was
failing to inject itself into the resulting Hash. This caused a `NoMethodError`
to be thrown when attempting to perform the action.

Now, we properly inject the mixin when necessary so the `#merge` method works.

1 files changed, 4 insertions, 2 deletions

diff --git a/lib/hashie/extensions/indifferent_access.rb b/lib/hashie/extensions/indifferent_access.rb
index 55648a6..e6e670a 100644
--- a/lib/hashie/extensions/indifferent_access.rb
+++ b/lib/hashie/extensions/indifferent_access.rb
@@ -133,8 +133,10 @@ module Hashie
         self
       end
 
-      def merge(*)
-        super.convert!
+      def merge(*args)
+        result = super
+        IndifferentAccess.inject!(result) if hash_lacking_indifference?(result)
+        result.convert!
       end
 
       def merge!(*)