encode static method Null safety

Implementation

static String? encode(APISecuritySchemeFlow? flow) {
  switch (flow) {
    case APISecuritySchemeFlow.authorizationCode:
      return "accessCode";
    case APISecuritySchemeFlow.password:
      return "password";
    case APISecuritySchemeFlow.implicit:
      return "implicit";
    case APISecuritySchemeFlow.application:
      return "application";
    default:
      return null;
  }
}