Missing optional variable in AND statement generates invalid Cypher query

[mrandrewhayes]

Describe the bug
When building a GraphQL query using WHERE... AND with variables inside the AND statement, omitting an optional variable results in a Cypher error.

By contrast, it is possible to omit optional variables that are used outside the AND statement. In that case the query runs and the whole term is ignored in the resulting Cypher query.

Type definitions

type Event {
    id: ID!
    name: String
    start: DateTime
    end: DateTime
    activity: String
}

To Reproduce

1. Use a server running Neo4j GraphQL 1.2.3 and a schema containing the above type definition
2. Use a client such as Apollo Client that can pass a GraphQL query with variables to the server
3. Run the query:

query ($rangeStart: DateTime, $rangeEnd: DateTime, $activity: String) {
  events (
    where: { 
      AND: [
        { start_GTE: $rangeStart }
        { start_LTE: $rangeEnd }
        { activity: $activity }
      ]
    }
  ) 
  {
    start
    activity
  }  
}            

with the variables

{
  "rangeStart": "2021-07-18T00:00:00+0100",
  "rangeEnd": "2021-07-18T23:59:59+0100"
}

... that is, omitting the optional variable $activity

Expected behavior
I would ideally like Event nodes with any value in the activity field to be included in the result

Actual result
The error message is returned to the client:

{
  "errors": [
    {
      "message": "Invalid input ')': expected whitespace, comment or an expression (line 2, column 85 (offset: 103))\n\"WHERE (this.start >= $this_AND_start_GTE AND this.start <= $this_AND1_start_LTE AND )\"\n                                                                                     ^",
      "locations": [
        {
          "line": 2,
          "column": 3
        }
      ],
      "path": [
        "events"
      ],
      "extensions": {
        "code": "INTERNAL_SERVER_ERROR",
        "exception": {
          "code": "Neo.ClientError.Statement.SyntaxError",
          "name": "Neo4jError"
        }
      }
    }
  ],
  "data": null
}

System (please complete the following information):

• Windows
• @neo4j/graphql@1.2.3
• node 14.16.1

[mrandrewhayes]

Working perfectly in 1.2.4. Nice work! 🦅