Example config.yaml: postprocessed_with_variables route fails when result is empty

[thomas-delva]

Error description

In the config.yaml, when a non-existent actor gets passed to the route /movies/{actor}/postprocessed_with_variables, a 500 error is thrown:

debug 2020-08-28T12:47:25.992Z : {"data":{"query":"{ id @single ... on Film { starring(label: \"Bradd Pitt\") @single }}"}}
verbose 2020-08-28T12:47:26.001Z : {"data":[{}]}
Pipe module error: Cannot read property 'match' of undefined
info 2020-08-28T12:47:26.002Z : GET /movies/Bradd%20Pitt/postprocessed_with_variables 500 9.909 ms - 1084

How to reproduce

1. Start Walder version 2.0.2 with the command yarn start -c example/config.yaml -l debug --no-cache
2. Surf to http://localhost:3000/movies/Bradd%20Pitt/postprocessed_with_variables (Notice Brad Pitt is misspelled.)

[pheyvaer]

This is seems like an issue with the GraphQL-LD library.