[JavaSpring] multipart/form-data defined with required part is optional in the generated Java Spring Code

Description

When the OpenAPI 3.0 YAML definition contains a multipart/form-data with a part defined as required, then the generated server-side interface defines the given part as optional (required = false).

Swagger-codegen version

3.0.18

Swagger declaration file content or url

openapi: 3.0.0
info:
  title: "testbug"
  version: "0.1"
paths:
  /testbug/:
    post:
      requestBody:
        content:
          multipart/form-data:
            schema:
              properties:
                myPart:
                  type: object
              required:
                - myPart
      responses:
        "200":
          description: OK

Command line used for generation

java -jar swagger-codegen-cli-3.0.18.jar generate -l spring -o output -i swagger.yaml

Steps to reproduce

Run above command on above OpenAPI 3.0 YAML content and check generated file output/src/main/java/io/swagger/api/TestbugApi.java

Related issues/PRs

N/A

Suggest a fix/enhancement

Root cause not known.

Run the supplied swagger-codegen-cli 3.0.18 command with the YAML example and inspect output/src/main/java/io/swagger/api/TestbugApi.java. Trace how the multipart/form-data schema's required list is handled before the Spring interface is generated. Done means the generated part reflects the OpenAPI requirement with required=true.