Specifying variables object in query param results in 500 error

[gryphonmyers]

Repro Steps:

1. Send a GET request to /cockpit/api/graphql/query specifying valid gql "query" parameter per specification at: https://graphql.org/learn/serving-over-http/
2. Note that the query is parsed correctly, and response is sent as expected.
3. Send another GET request, this time adding the additional "variables" query parmeter in JSON-encoded format (e.g. "{}").
4. Note that a 500 error response is sent.

Expected results: Supplying variables should not cause the application to error when sending them in a query parameter