code: void returnDBConnection(DBConn dbConn) {
          if (dbConn == null) {
              return;
          }
          
          if (!getState().isRunning()) {
              dbConn.close();     // from straggler thread; close and discard
          } else if (dbConn.isFailed()) {
              // Purge all connections in case a Cassandra node is now dead.
              dbConn.close();
              m_logger.info("Purging database connection pool");
              purgeAllConnections();
          } else {
              returnGoodConnection(dbConn);
          }
      }
docs: is null -- this reduces checking in "finally" blocks.