TypeError: Cannot read properties of null (reading 'reduce') when using getTreatmentsWithConfig with rule-based segments (proxy 5.11.0+)

[etremblay]

Description

Upgrading the Split Proxy from 5.10.3 to 5.11.0+ (tested up to 5.12.7) causes an unhandled TypeError crash when getTreatmentsWithConfig is called and one or more feature flags use rule-based segments.

The error is thrown synchronously during SDK evaluation on SDK_READY, crashing the evaluation of all treatments in the batch.

Error

Uncaught TypeError: Cannot read properties of null (reading 'reduce')
    at getTreatment
    at eo
    at to (forEach)
    at Qr
    at getTreatmentsWithConfig
    at getTreatmentsWithConfig
    at onReady

Versions

Package	Version
@splitsoftware/splitio	11.11.2
@splitsoftware/splitio-redux	2.3.0
Split Proxy (working)	5.10.3
Split Proxy (broken)	5.11.0 – 5.12.7

Steps to Reproduce

1. Configure the JS SDK (11.11.2) to point at a Split Proxy.
2. Create a feature flag that uses a rule-based segment (introduced in proxy 5.11.0).
3. Upgrade the proxy from 5.10.3 to 5.11.0 or later.
4. On SDK ready, call getTreatmentsWithConfig([...]) with a flag that uses a rule-based segment.
5. Observe the TypeError crash.

Root Cause Analysis

The crash originates in javascript-commons at src/evaluator/matchers/rbsegment.ts.

The IRBSegment DTO type explicitly allows null for several nested fields:

// src/dtos/types.ts
export interface IRBSegment extends TargetingEntity {
  excluded?: {
    keys?: string[] | null,
    segments?: IExcludedSegment[] | null
  } | null
}

Proxy 5.11.0 introduced rule-based segments and may return null values for excluded, excluded.keys, or excluded.segments in the segment payload. The evaluator guards with || [] / || {} which handles undefined but the crash surfaces deeper in the condition evaluation pipeline — inside the parser called from matchConditions — where a matcher data array arrives as null and .reduce() is called on it without a null guard.

// rbsegment.ts – isExcluded
const excluded = rbSegment.excluded || {};          // guards undefined/null ✅
return (excluded.segments || []).reduce(...)        // guards undefined/null ✅

// BUT inside matchConditions → parser → condition matchers:
// a matcher data property (e.g. whitelistMatcherData.whitelist) 
// can arrive as null from the proxy, and .reduce() is called without a null guard

Expected Behavior

getTreatmentsWithConfig should handle null arrays in rule-based segment condition matcher data gracefully, returning 'control' rather than throwing an uncaught TypeError.

Actual Behavior

An uncaught TypeError: Cannot read properties of null (reading 'reduce') is thrown, crashing the entire getTreatmentsWithConfig call and all downstream treatment evaluations.

Workaround

Pin the Split Proxy to 5.10.3 until a fix is available.