[Bug]: TypeScript payloads preset emits non-compiling code (non-nullable date-time null fallback + nullable-array marshal)

[ALagoni97]

Description

Generating a TypeScript client from an OpenAPI spec produces payloads files that fail tsc. Generation reports zero errors; the breakage only appears when the generated package is built. Two independent defects in the payloads preset:

1. unmarshal() emits an unconditional null fallback for date-time fields.
For a required (non-nullable) date-time property the declared type is Date, but the deserializer produces Date | null.

TS2322: Type 'Date | null' is not assignable to type 'Date'.

2. marshal() guards a nullable array/object with !== undefined only, then iterates it.
For a type: ["null", "array"] property the field is T[] | null, so null slips past the guard.

TS2531: Object is possibly 'null'.

Environment

• CLI Version: 0.72.0 (latest)
• Node Version: v22.14.0
• OS: Windows 11

Minimal Reproduction

codegen.ts

import { TheCodegenConfiguration } from '@the-codegen-project/cli'

const config: TheCodegenConfiguration = {
  inputType: 'openapi',
  inputPath: './input.openapi.json',
  language: 'typescript',
  generators: [{ preset: 'payloads', outputPath: './src/payloads', serializationType: 'json' }],
}

export default config

input.openapi.json

{
  "openapi": "3.1.1",
  "info": { "title": "Payloads repro", "version": "1.0.0" },
  "paths": {
    "/thing": {
      "get": {
        "operationId": "getThing",
        "responses": {
          "200": {
            "description": "OK",
            "content": { "application/json": { "schema": { "$ref": "#/components/schemas/Thing" } } }
          }
        }
      }
    }
  },
  "components": {
    "schemas": {
      "Thing": {
        "type": "object",
        "required": ["created"],
        "properties": {
          "created": { "type": "string", "format": "date-time" },
          "signers": { "type": ["null", "array"], "items": { "type": "string" } }
        }
      }
    }
  }
}

Command

the-codegen-project generate && tsc --noEmit

Actual Output

Thing.ts:

private _created: Date;                 // required -> non-null
private _signers?: string[] | null;

public marshal(): string {
  // ...
  if(this.signers !== undefined) {      // does not exclude null
    for (const unionItem of this.signers) {   // TS2531: Object is possibly 'null'
      // ...
    }
  }
}

public static unmarshal(json: string | object): Thing {
  const obj = typeof json === "object" ? json : JSON.parse(json);
  const instance = new Thing({} as any);
  if (obj["created"] !== undefined) {
    instance.created = obj["created"] == null ? null : new Date(obj["created"]);  // TS2322: Date | null -> Date
  }
  // ...
}

Expected Output

1. For a non-nullable date-time, drop the null branch so the value matches the declared Date:

instance.created = new Date(obj["created"]);

2. Guard nullable array/object marshalling against null too:

if (this.signers !== undefined && this.signers !== null) {
  for (const unionItem of this.signers) { /* ... */ }
}

Additional Context

• Discovered while publishing a real client; the publish pipeline runs npm run build (tsc) before npm publish, so these tsc errors abort publishing.
• The ajv / ajv-formats import errors seen in isolation resolve after npm i and are unrelated to these two defects.