The express-graphql reference implementation [provides a check]
(2e27a73358/src/index.js (L201-L208))
to protect against cases where a GET request is made that does not
have a `query` parameter where the GraphQL query would be present.
Without this guard, graphql-js's `parse` will return `undefined`
for the `DocumentNode` since it has no document to read. Subsequently
passing this to `isQueryOperation` results in a `TypeError`, because
we are providing `undefined` where `getOperationAst` [expects to get
a DocumentNode](5fe39262a3/src/utilities/getOperationAST.js (L19)).
A new test file is added for `runHttpQuery`, as one previously did
not seem to exist.
This fixes the default behavior for class-based contexts by also cloning the prototype, and it allows you to customize per-operation behavior by passing in a function as context.
