Fix empty mime type for ActiveStorage local file service [SCI-4360]

app/controllers/active_storage/direct_uploads_controller.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+module ActiveStorage
+  class DirectUploadsController < CustomBaseController
+    def create
+      blob = ActiveStorage::Blob.create_before_direct_upload!(blob_args)
+      render json: direct_upload_json(blob)
+    end
+
+    private
+
+    def blob_args
+      args = params.require(:blob)
+                   .permit(:filename, :byte_size, :checksum, :content_type, :metadata)
+                   .to_h
+                   .symbolize_keys
+      args[:content_type] = 'application/octet-stream' if args[:content_type].blank?
+      args
+    end
+
+    def direct_upload_json(blob)
+      blob.as_json(root: false, methods: :signed_id)
+          .merge(direct_upload: { url: blob.service_url_for_direct_upload,
+                                  headers: blob.service_headers_for_direct_upload })
+    end
+  end
+end