code: private String getEngineString(@Nullable DatabaseEngine engine) {
          if( engine == null ) {
              return AWS_ENGINE_MYSQL;
          }
          switch( engine ) {
              case ORACLE_SE1: return AWS_ENGINE_ORACLE_SE1;
              case ORACLE_SE: return AWS_ENGINE_ORACLE_SE;
              case ORACLE_EE: return AWS_ENGINE_ORACLE_EE;
              case SQLSERVER_SE: return AWS_ENGINE_SQLSERVER_SE;
              case SQLSERVER_EE: return AWS_ENGINE_SQLSERVER_EE;
              case SQLSERVER_EX: return AWS_ENGINE_SQLSERVER_EX;
              case SQLSERVER_WEB: return AWS_ENGINE_SQLSERVER_WEB;
              case POSTGRES: return AWS_ENGINE_POSTGRES;
              case MYSQL:
              default: return AWS_ENGINE_MYSQL;
          }
      }
docs: Get Amazon-specific engine name
  @param engine database engine
  @return Amazon-spefic engine name, returns 'MySQL' if engine was null.