fix(hql): DROP operation on empty traversals

[ishaksebsib]

Description

This PR fixes a runtime error in DROP operations when attempting to drop non-existent nodes, ensuring graceful handling of empty traversals.

Problem

Queries like DROP N<NodeType>(id) on non-existent IDs failed with "Conversion error: Incorrect Type: Empty" because drop_traversal did not handle TraversalValue::Empty returned by collect_to_obj().

Solution

Added TraversalValue::Empty => Ok(()), in the match statement of drop_traversal. This treats empty traversals as successful no-ops.

Related Issues

None

Checklist when merging to main

• No compiler warnings (if applicable)
• Code is formatted with rustfmt
• No useless or dead code (if applicable)
• Code is easy to understand
• Doc comments are used for all functions, enums, structs, and fields (where appropriate)
• All tests pass
• Performance has not regressed (assuming change was not to fix a bug)
• Version number has been updated in helix-cli/Cargo.toml and helixdb/Cargo.toml

Additional Notes

curl -X POST http://localhost:6969/DeleteNode \
      -H "Content-Type: application/json" \
      -d '{
      "node_id": "550e8400-e29b-41d4-a716-446655440007"
      }'

Conversion error: Incorrect Type: Empty⏎

Greptile Overview

Updated On: 2025-10-24 19:24:02 UTC

Greptile Summary

Fixed runtime error when attempting to DROP non-existent nodes by adding TraversalValue::Empty => Ok(()) case to the match statement in drop_traversal().

• Resolved "Conversion error: Incorrect Type: Empty" error when dropping nodes by ID that don't exist
• Empty traversals now treated as successful no-ops, consistent with how other parts of the codebase handle TraversalValue::Empty
• Minor formatting improvements applied to let-chain syntax for consistency

Important Files Changed

File Analysis

Filename	Score	Overview
helix-db/src/helix_engine/traversal_core/ops/util/drop.rs	5/5	Added handling for TraversalValue::Empty case in drop_traversal to gracefully handle dropping non-existent nodes; minor formatting fixes applied

Sequence Diagram

sequenceDiagram
    participant Client
    participant HQL
    participant drop_traversal
    participant collect_to_obj
    participant Storage

    Client->>HQL: DROP N<NodeType>(non_existent_id)
    HQL->>collect_to_obj: Query for node by ID
    collect_to_obj->>Storage: Fetch node
    Storage-->>collect_to_obj: No results found
    collect_to_obj-->>HQL: TraversalValue::Empty
    HQL->>drop_traversal: Process traversal items
    alt Empty traversal (after fix)
        drop_traversal-->>HQL: Ok(()) - no-op
        HQL-->>Client: Success
    else Empty traversal (before fix)
        drop_traversal-->>HQL: ConversionError
        HQL-->>Client: Error: "Incorrect Type: Empty"
    end

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