 GraphQLError: Upload serialization unsupported.
I have the same problem with this error, help me please with more information
 // query mutation
mutation Mutation($upload: Upload!) {
  singleUpload(file: $upload) {
    encoding
    filename
    mimetype
  }
}

//response
{
    "errors": [
        {
            "message": "Upload serialization unsupported.",
            "locations": [
                {
                    "line": 2,
                    "column": 3
                }
            ],
            "path": [
                "singleUpload"
            ],
            "extensions": {
                "code": "INTERNAL_SERVER_ERROR",
                "exception": {
                    "message": "Upload serialization unsupported.",
                    "stacktrace": [
                        "GraphQLError: Upload serialization unsupported.",
                        "    at GraphQLScalarType.serialize (/Users/omar-imac/Desktop/DesarrolloProyectos/1.-1Mentor/pilot-backend/node_modules/graphql-upload/public/GraphQLUpload.js:88:11)",
                        "    at /Users/omar-imac/Desktop/DesarrolloProyectos/1.-1Mentor/pilot-backend/node_modules/@graphql-tools/delegate/dist/utils/src/transformInputValue.js:27:57",
                        "    at transformInputValue (/Users/omar-imac/Desktop/DesarrolloProyectos/1.-1Mentor/pilot-backend/node_modules/@graphql-tools/delegate/dist/utils/src/transformInputValue.js:8:52)",
                        "    at Object.serializeInputValue (/Users/omar-imac/Desktop/DesarrolloProyectos/1.-1Mentor/pilot-backend/node_modules/@graphql-tools/delegate/dist/utils/src/transformInputValue.js:27:12)",
                        "    at /Users/omar-imac/Desktop/DesarrolloProyectos/1.-1Mentor/pilot-backend/dist/delegate/src/createRequest.js:59:37",
                        "    at Array.forEach (<anonymous>)",
                        "    at createRequest (/Users/omar-imac/Desktop/DesarrolloProyectos/1.-1Mentor/pilot-backend/dist/delegate/src/createRequest.js:55:29)",
                        "    at createRequestFromInfo (/Users/omar-imac/Desktop/DesarrolloProyectos/1.-1Mentor/pilot-backend/dist/delegate/src/createRequest.js:13:12)",
                        "    at Object.delegateToSchema (/Users/omar-imac/Desktop/DesarrolloProyectos/1.-1Mentor/pilot-backend/dist/delegate/src/delegateToSchema.js:12:21)",
                        "    at /Users/omar-imac/Desktop/DesarrolloProyectos/1.-1Mentor/pilot-backend/dist/wrap/src/generateProxyingResolvers.js:64:47"
                    ]
                }
            }
        }
    ],
    "data": null
}