Error when processing uploads after upgrading to v10
I'm testing graphql-upload with graphql-relay / mutationWithClientMutationId. However, the return value is {}

Any solution?

![mutation](https://user-images.githubusercontent.com/26548220/73503052-cd3bbe00-43a9-11ea-8ad6-cf9ef1c5f5f3.png)

![Altair](https://user-images.githubusercontent.com/26548220/73503120-1ab82b00-43aa-11ea-8723-a8ad035fe025.png)

