Fix null issue when parsing search request attributes

[CascadingRadium]

• We allow parsing a few attributes of the search request as json.RawMessage like
  • KNN Params
  • KNN Filter
  • PresearchData
• It is possible for the JSON body to contain the keyword null for these attributes, especially after a marshal-unmarshal cycle.
• This null value is passed on downstream, causing every check for len(attribute) > 0 to succeed and take the path for which the attribute is valid even if the attribute is actually nil.
• Fix this issue by adding a custom type that parses null specially and sets the attribute to nil when required.

[coveralls]

coverage: 51.666% (-0.02%) from 51.682% — nullIssue into master

[Copilot]

Pull request overview

This PR addresses an edge case in SearchRequest JSON parsing where attributes stored as json.RawMessage can retain the literal bytes "null" after decoding, causing downstream len(...) > 0 checks to behave as if the attribute is present. It introduces a custom raw-message wrapper to treat JSON null as an unset/nil value during unmarshalling.

Changes:

• Introduce OptionalRawMessage to decode JSON null (and empty) into nil, preventing "null" payloads from being treated as present.
• Update SearchRequest.UnmarshalJSON (vectors + non-vectors) to use OptionalRawMessage for params and pre_search_data, and similarly for KNN params/filter.
• Add a vectors-mode regression test covering knn[].params: null and knn[].filter: null, including a marshal/unmarshal round-trip.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
search.go	Adds OptionalRawMessage wrapper type for json.RawMessage-like decoding with special null handling.
search_knn.go	Uses OptionalRawMessage in vectors-mode SearchRequest parsing for KNN/raw attributes; also adjusts JSON tags.
search_no_knn.go	Uses OptionalRawMessage in non-vectors SearchRequest parsing for raw attributes; also adjusts JSON tags.
search_knn_test.go	Adds vectors-mode test coverage for KNN null params/filter (and round-trip behavior).

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.