Array of binary strings (multiple file upload) generates List<String> instead of List<MultipartFile>

[joseegman-idoneea]

Description

When an OpenAPI schema declares an array of binary strings (multiple file upload), the generator maps the array items to String instead of MultipartFile, producing List<String> in the generated model.

A single binary property is handled correctly (MultipartFile), so only the array/collection case is affected.

Steps to reproduce

Given a schema property such as:

Document:
  type: object
  properties:
    document:
      type: string
      format: binary
    attachments:
      type: array
      items:
        type: string
        format: binary

Actual result

private MultipartFile document;        // OK
private List<String> attachments;      // wrong

Expected result

private MultipartFile document;
private List<MultipartFile> attachments;

Root cause

ModelBuilder.processArray(...) resolves the element type of a simple (non-$ref, non-composed, no-properties) array item through MapperUtil.getSimpleType(items, ...). getSimpleType has no binary detection (it never calls ApiTool.isBinary), so a { type: string, format: binary } item falls through to "string".

Binary → MultipartFile is only applied for scalar object properties, in ModelBuilder.processStringProperty(...), never for array items.

The same gap applies to the OpenAPI 3.1 style (contentEncoding / contentMediaType), since ApiTool.isBinary already covers both but is not consulted on the array path.

Environment

• Affects the OpenAPI code generator (multiapi-engine).
• Reproduced on main.