Should throw error when a JSON instead of a File is received from client
When I send a JSON (number, string, object, etc) instead of a File from client, I don't get any errors and the argument returns a JS Object instead of [Promise\<FileUpload\>](https://github.com/jaydenseric/graphql-upload#type-fileupload).  
Is this working correctly? Shouldn't this throw an error in the `parseValue` of scalar? We are expecting a stream after all.  
This forces us to validate the input every time we are using `Upload` scalar.  

I'm using Apollo Server (and `apollo-upload-client` which does not matter in this scenario)