[Bug] type: ["null", "object"] with additionalProperties generates object instead of Record<string, string>

[7amou3]

Summary

swagger-typescript-api does not correctly interpret OpenAPI 3.1 schemas that use a nullable object type expressed as a union:

{
  "type": ["null", "object"],
  "additionalProperties": { "type": "string" }
}

This is valid OpenAPI 3.1 syntax, and indicates: a nullable object whose keys are strings and whose values are strings.

However, the current generator outputs:

  labels?: null | object;

Which loses all typing information.

Expected Output

labels?: Record<string, string> | null;

Actual Output

labels?: null | object;

Why This Is Incorrect

• "object" with "additionalProperties": { "type": "string" } should always map to Record<string, string>.

• Wrapping "type": ["null", "object"] should become Record<string, string> | null.

• Instead, the union collapses to generic object, discarding key/value types.

Minimal Reproduction

{
  "openapi": "3.1.0",
  "components": {
    "schemas": {
      "Test": {
        "type": ["null", "object"],
        "additionalProperties": { "type": "string" }
      }
    }
  }
}

Generated TypeScript:

export type Test = null | object;

Expected:

export type Test = Record<string, string> | null;

Root of the Issue

The generator appears to:

• Recognize "type": "object" case

• But not recognize "type": ["object"] or "type": ["null", "object"] cases

• And therefore falls back to generic object

This breaks any nullable dictionary schema.

Impact

All APIs using OpenAPI 3.1 unions for nullable dictionaries generate unsafe and incorrect TypeScript definitions