add to_s to query

Author: xuorig

app/controllers/graphql_controller.rb

@@ -1,6 +1,6 @@
 class GraphqlController < ApplicationController
   def execute
-    query_string = params[:query]
+    query_string = params[:query].to_s
     variables = ensure_hash(params[:variables])
     result = ::Graph::Schema.execute(query_string, variables: variables)
     render json: result