required of schema in multipart/form-data not supported

how to produce

using this openapi.json

{
  "openapi": "3.0.1",
  "info": {
    "title": "OpenAPI definition",
    "version": "v0"
  },
  "servers": [
    {
      "url": "http://localhost:8080",
      "description": "Generated server url"
    }
  ],
  "tags": [
    {
      "name": "File",
      "description": "upload"
    }
  ],
  "paths": {
    "/files": {
      "post": {
        "tags": [
          "File"
        ],
        "summary": "upload single file",
        "operationId": "uploadFile",
        "parameters": [
          {
            "name": "bucket",
            "in": "query",
            "description": "bucket name",
            "required": false,
            "schema": {
              "type": "string"
            }
          }
        ],
        "requestBody": {
          "content": {
            "multipart/form-data": {
              "schema": {
                "required": [
                  "file"
                ],
                "type": "object",
                "properties": {
                  "file": {
                    "type": "string",
                    "description": "file to upload",
                    "format": "binary"
                  }
                }
              }
            }
          }
        },
        "responses": {
          "200": {
            "description": "OK"
          }
        }
      }
    }
  }
}

will generate the wrong result

    /**
     * upload single file
     * @param {Object} opts Optional parameters
     * @param {Blob} opts.file 
     * @param {String} opts.bucket bucket name
     * @return {Promise} a {@link https://www.promisejs.org/|Promise}
     */
    uploadFile(opts) {
      return this.uploadFileWithHttpInfo(file, opts)
        .then(function(response_and_data) {
          return response_and_data.data;
        });
    }

The correct result should be

    /**
     * upload single file
     * @param {Blob} file 
     * @param {Object} opts Optional parameters
     * @param {String} opts.bucket bucket name
     * @return {Promise} a {@link https://www.promisejs.org/|Promise}
     */
    uploadFile(file, opts) {
      return this.uploadFileWithHttpInfo(file, opts)
        .then(function(response_and_data) {
          return response_and_data.data;
        });
    }

fix

Index: src/main/java/io/swagger/codegen/v3/generators/DefaultCodegenConfig.java
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/src/main/java/io/swagger/codegen/v3/generators/DefaultCodegenConfig.java b/src/main/java/io/swagger/codegen/v3/generators/DefaultCodegenConfig.java
--- a/src/main/java/io/swagger/codegen/v3/generators/DefaultCodegenConfig.java	(revision 3ed70aeca12709c5b2929c6c4ae4cdc2a4ee2299)
+++ b/src/main/java/io/swagger/codegen/v3/generators/DefaultCodegenConfig.java	(revision 1c8f728b2f01ee0f23cdf042b14db87dd4241da2)
@@ -2178,13 +2178,14 @@
                     continue;
                 }
                 if (isForm) {
+                    final List<String> schemaRequired = schema.getRequired();
                     final Map<String, Schema> propertyMap = schema.getProperties();
                     boolean isMultipart = contentType.equalsIgnoreCase("multipart/form-data");
                     if (propertyMap != null && !propertyMap.isEmpty()) {
                         for (String propertyName : propertyMap.keySet()) {
                             CodegenParameter formParameter = fromParameter(new Parameter()
                                     .name(propertyName)
-                                    .required(body.getRequired())
+                                    .required(body.getRequired() != null && body.getRequired() || schemaRequired.contains(propertyName))
                                     .schema(propertyMap.get(propertyName)), imports);
                             if (isMultipart) {
                                 formParameter.getVendorExtensions().put(CodegenConstants.IS_MULTIPART_EXT_NAME, Boolean.TRUE);
@@ -2192,7 +2193,7 @@
                             // todo: this segment is only to support the "older" template design. it should be removed once all templates are updated with the new {{#contents}} tag.
                             formParameter.getVendorExtensions().put(CodegenConstants.IS_FORM_PARAM_EXT_NAME, Boolean.TRUE);
                             operationParameters.addFormParam(formParameter.copy());
-                            if (body.getRequired() != null && body.getRequired()) {
+                            if (formParameter.getRequired()) {
                                 operationParameters.addRequiredParam(formParameter.copy());
                             }
                             operationParameters.addAllParams(formParameter);

Start in src/main/java/io/swagger/codegen/v3/generators/DefaultCodegenConfig.java at the form-parameter handling, and compare the supplied multipart/form-data schema with the generated JavaScript signature. Done when the required file is emitted as a direct file argument while the optional bucket remains in opts, matching the expected output.