NullPointerException with Empty items Field in OpenAPI Spec

[erblsqa]

I'm running contract tests using CATS and encountered an issue when array definitions in the OpenAPI specification have an empty items field or are missing it entirely. This causes a NullPointerException and crashes the test process.

For example, this field in the OpenAPI spec:

"QueryRestarted": {
  "example": [],
  "items": {},
  "maxItems": 0,
  "type": "array"
}

The items field is present but empty, which leads to the error. The empty items field should be considered valid according to OpenAPI, but it causes the tests to fail unexpectedly with CATS.

Steps to Reproduce:

1. Define an array in the OpenAPI specification with an empty items field or a missing items field.
2. Run the contract tests using CATS.
3. Observe the NullPointerException error.

Expected Behavior:
CATS should be able to handle an empty or missing items field without crashing. The spec itself should be considered valid.

Actual Behavior:
CATS throws a NullPointerException, which results in the test process crashing.

Suggested Action:
We would appreciate it if you could investigate the issue with the empty items field causing a NullPointerException and suggest any workarounds or fixes for handling this scenario in CATS.

Thank you!

[en-milie]

Hi @erblsqa. I'm not able to reproduce it. I've tried with your above schema both in request and response, with empty or missing items, but didn't get any NullPointerException. Would it be possible to post part of the OpenAPI file that you're using?

[erblsqa]

Hi @en-milie , thanks for checking. I’ll share the part of the OpenAPI file that triggered the error on my end. The issue seems to occur when the schema defines an array but the items field is either missing or left empty, like this:

Example 1 - StatusArray:

{
  "components": {
    "schemas": {
      "EventData": {
        "oneOf": [
          {
            "properties": {
              "StatusArray": {
                "example": [],
                "items": {},           // ⚠️ PROBLEM: Empty items object
                "maxItems": 0,
                "type": "array"
              }
            }
          }
        ]
      }
    }
  }
}

Example 2 - StatusArray:

{
  "properties": {
    "StatusArray": {
      "example": [],
      "items": {},               // ⚠️ PROBLEM: Empty items object
      "maxItems": 0,
      "type": "array"
    }
  }
}

Example 3 - DataResponse:

{
  "components": {
    "schemas": {
      "DataResponse": {
        "properties": {
          "data": {
            "items": {
              "items": {},           // ⚠️ PROBLEM: Empty items object in nested array
              "type": "array"
            },
            "type": "array"
          }
        }
      }
    }
  }
}