Accept null as graphql query variables

[firesharker]

Issue

Ajv schema validation fails if graphql query variables is null.
For example {"query":"{ users { email } }","variables":null} returns

[
  {
    "keyword": "type",
    "dataPath": ".variables",
    "schemaPath": "#/properties/variables/type",
    "params": {
      "type": "object"
    },
    "message": "should be object"
  }
]

Solution and steps

Update Ajv schema to accept null for variables.

[LoicPoullain]

In which situation would you like to send a null value? It does not seem to be required by GraphQL clients or the GraphQL recommendation: https://graphql.org/learn/serving-over-http/#post-request.

If it does, then we'll need to add also a unit test and maybe update GraphQLController.post

[firesharker]

GraphiQL sends it by default if you do not write anything in the query variables tab. Previously we used apollo-server without FoalTS, and it accepts null. I could not find anything about whenever it should be accepted or not, so I assumed that probably it is a good idea to be consistent with them.

[LoicPoullain]

Ok, this is legitimate.

I added a test to your branch to make sure that it works as expected.

[LoicPoullain]

Weirdly the Travis web hook is not triggered. I'll need to fix it before merging the PR.

[LoicPoullain]

👍