(GraphQL) error when ids is not a list

[MichaelJCompton]

What version of Dgraph are you using?

dgraph graphql standalone

Steps to reproduce the issue (command/config used to run Dgraph).

https://discuss.dgraph.io/t/graphql-delete-mutation-internal-server-error-a-panic-was-trapped/5544

Expected behaviour and actual result.

Should return a validation error.

[MichaelJCompton]

Looks like a validation error on the parser library.

[MichaelJCompton]

fixed by #4480