[BUG] NPE in DefaultGenerator.getOAuthMethods

Created by: kymbalon

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• [x ] Have you validated the input using an OpenAPI validator (example)?
• [x ] What's the version of OpenAPI Generator used?
• [x ] Have you search for related issues/PRs?
• [x ] What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

DefaultGenerator.getOAuthMethods iterates a list of CodegenSecurity querying the Boolean (object) isOAuth without checking it for null. Maybe there are similar places in the code where Boolean variables should be double-checked (or auto-boxed).

openapi-generator version

4.0.0-beta2

OpenAPI declaration file content or url

components:
  securitySchemes:
    BasicAuth:
      type: http
      scheme: basic
    BearerAuth:
      type: http
      scheme: bearer
    ApiKeyAuth:
      type: apiKey
      in: header
      name: X-API-Key
    OpenID:
      type: openIdConnect
      openIdConnectUrl: https://example.com/.well-known/openid-configuration
    OAuth2:
      type: oauth2
      flows:
        authorizationCode:
          authorizationUrl: https://example.com/oauth/authorize
          tokenUrl: https://example.com/oauth/token
          scopes:
            read: Grants read access
            write: Grants write access
            admin: Grants access to admin operations

Command line used for generation

Steps to reproduce

API spec with at least one securityScheme which is not OAuth2.

Related issues/PRs

Other issues concerning NPEs might be related.

Suggest a fix

    for (CodegenSecurity cs : authMethods) {
        if (Boolean.TRUE.equals(cs.isOAuth)) {
            oauthMethods.add(cs);
        }
    }