Fix serializeRecord to handle null/undefined additionalProperties

[Copilot]

Fix SerializeRecord to handle null and undefined for additional properties

Summary

This PR fixes an issue where generated serializer functions would fail when additionalProperties is null or undefined.

Problem

When TypeSpec generates TypeScript serializer functions for models with additional properties, it calls serializeRecord(item.additionalProperties). The serializeRecord function internally calls Object.keys(item), which throws a TypeError if item is null or undefined:

TypeError: Cannot convert undefined or null to object

Solution

Modified the code generation in buildSerializerFunction.ts to add a nullish coalescing operator (?? {}), so the generated code becomes:

...serializeRecord(item.additionalProperties ?? {})

This ensures that an empty object is passed to serializeRecord when additionalProperties is null or undefined, preventing the runtime error.

Changes Made

1. ✅ Updated packages/typespec-ts/src/modular/serialization/buildSerializerFunction.ts to add ?? {} when generating serializeRecord calls (line 476)
2. ✅ Updated test expectations in:
   • packages/typespec-ts/test/modularUnit/scenarios/models/serialization/additionalProperties.md (7 test cases)
   • packages/typespec-ts/test/modularUnit/scenarios/modelsGenerator/modelsGenerator.md (1 test case)
3. ✅ Regenerated smoke test files to verify the fix works correctly in all generated code

Validation

• ✅ All 384 unit tests pass
• ✅ Code properly formatted with rush format
• ✅ Code properly linted with npm run lint
• ✅ Code review passed with no issues
• ✅ Security scan passed (CodeQL)
• ✅ Smoke test passed - all specs succeeded (8m 48s)

Fix Verification

The fix follows the suggestion from @MaryGao in the original issue and ensures that:

• When additionalProperties is defined: normal behavior (serialize the properties)
• When additionalProperties is null or undefined: safely pass an empty object to serializeRecord, which returns {}
• No runtime errors occur

Generated Code Example

The smoke test regenerated files showing the fix working correctly:

// Before:
export function chatCompletionFunctionParametersSerializer(item: ChatCompletionFunctionParameters): any {
  return { ...serializeRecord(item.additionalProperties) };  // Would fail if null/undefined
}

// After:
export function chatCompletionFunctionParametersSerializer(item: ChatCompletionFunctionParameters): any {
  return { ...serializeRecord(item.additionalProperties ?? {}) };  // Safe with fallback
}

Original prompt

---

This section details on the original issue you should resolve

<issue_title>SerializeRecord does not support null and undefined for additional properties</issue_title>
<issue_description>https://github.com/Azure/autorest.typescript/blob/main/packages/typespec-ts/static/static-helpers/serialization/serialize-record.ts#L1

generate code link https://github.com/Azure/azure-sdk-for-js/blob/5fb686dc69ffda063beb131cc0fe110bed3cbcdc/sdk/redis/arm-rediscache/src/models/models.ts#L873:

export interface RedisCommonPropertiesRedisConfiguration {
  /** Specifies whether the RDB backup is enabled */
  rdbBackupEnabled?: string;
  /** Specifies the frequency for creating rdb backup in minutes. Valid values: (15, 30, 60, 360, 720, 1440) */
  rdbBackupFrequency?: string;
  /** Specifies the maximum number of snapshots for rdb backup */
  rdbBackupMaxSnapshotCount?: string;
  /** The storage account connection string for storing rdb file */
  rdbStorageConnectionString?: string;
  /** Specifies whether the aof backup is enabled */
  aofBackupEnabled?: string;
  /** First storage account connection string */
  aofStorageConnectionString0?: string;
  /** Second storage account connection string */
  aofStorageConnectionString1?: string;
  /** Value in megabytes reserved for fragmentation per shard */
  maxfragmentationmemoryReserved?: string;
  /** The eviction strategy used when your data won't fit within its memory limit. */
  maxmemoryPolicy?: string;
  /** Value in megabytes reserved for non-cache usage per shard e.g. failover. */
  maxmemoryReserved?: string;
  /** Value in megabytes reserved for non-cache usage per shard e.g. failover. */
  maxmemoryDelta?: string;
  /** The max clients config */
  readonly maxclients?: string;
  /** The keyspace events which should be monitored. */
  notifyKeyspaceEvents?: string;
  /** Preferred auth method to communicate to storage account used for data archive, specify SAS or ManagedIdentity, default value is SAS */
  readonly preferredDataArchiveAuthMethod?: string;
  /** Preferred auth method to communicate to storage account used for data persistence, specify SAS or ManagedIdentity, default value is SAS */
  preferredDataPersistenceAuthMethod?: string;
  /** Zonal Configuration */
  readonly zonalConfiguration?: string;
  /** Specifies whether the authentication is disabled. Setting this property is highly discouraged from security point of view; you should never disable authentication using this property! */
  authnotrequired?: string;
  /** SubscriptionId of the storage account for persistence (aof/rdb) using ManagedIdentity. */
  storageSubscriptionId?: string;
  /** Specifies whether AAD based authentication has been enabled or disabled for the cache */
  aadEnabled?: string;
  /** Additional properties */
  additionalProperties?: Record<string, any>;
}
export function redisCommonPropertiesRedisConfigurationSerializer(
  item: RedisCommonPropertiesRedisConfiguration,
): any {
  return {
    ...serializeRecord(item.additionalProperties),
    "rdb-backup-enabled": item["rdbBackupEnabled"],
    "rdb-backup-frequency": item["rdbBackupFrequency"],
    "rdb-backup-max-snapshot-count": item["rdbBackupMaxSnapshotCount"],
    "rdb-storage-connection-string": item["rdbStorageConnectionString"],
    "aof-backup-enabled": item["aofBackupEnabled"],
    "aof-storage-connection-string-0": item["aofStorageConnectionString0"],
    "aof-storage-connection-string-1": item["aofStorageConnectionString1"],
    "maxfragmentationmemory-reserved": item["maxfragmentationmemoryReserved"],
    "maxmemory-policy": item["maxmemoryPolicy"],
    "maxmemory-reserved": item["maxmemoryReserved"],
    "maxmemory-delta": item["maxmemoryDelta"],
    "notify-keyspace-events": item["notifyKeyspaceEvents"],
    "preferred-data-persistence-auth-method": item["preferredDataPersistenceAuthMethod"],
    authnotrequired: item["authnotrequired"],
    "storage-subscription-id": item["storageSubscriptionId"],
    "aad-enabled": item["aadEnabled"],
  };
}
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
<comment_new><author>@MaryGao</author><body>
fix:

...serializeRecord(item.additionalProperties ?? {}),

</comments>

• Fixes SerializeRecord does not support null and undefined for additional properties #3574

---

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[v-jiaodi]

@copilot Run smoke test to fix ci under folder packages/typespec-test.

[Copilot]

@copilot Run smoke test to fix ci under folder packages/typespec-test.

Smoke test completed successfully. All specs passed and generated files have been updated with the fix. The change is in commit cf9fc76.