#vulnerable code 
                                public synchronized void deleteApiByPublicKey(String publicKey) {
        Connection conn = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;

        try {
            conn = this.dbConfig.getConnection();
            stmt = conn.prepareStatement("delete from api where publickey=?;");

            stmt.setString(1, publicKey);

            stmt.execute();

            this.cache.remove(publicKey);
            this.genericCache.remove(apiAllApiCacheKey);

        }
        catch(SQLException ex) {
            LOGGER.severe(" caught a " + ex.getClass() + "\n with message: " + ex.getMessage());
        }
        finally {
            Helpers.closeQuietly(rs);
            Helpers.closeQuietly(stmt);
            Helpers.closeQuietly(conn);
        }
    } 
                            #location 22 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public synchronized void deleteApiByPublicKey(String publicKey) {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;

        try {
            connection = this.dbConfig.getConnection();
            preparedStatement = connection.prepareStatement("delete from api where publickey=?;");

            preparedStatement.setString(1, publicKey);

            preparedStatement.execute();
        }
        catch(SQLException ex) {
            Singleton.getLogger().severe(" caught a " + ex.getClass() + "\n with message: " + ex.getMessage());
        }
        finally {
            Helpers.closeQuietly(resultSet);
            Helpers.closeQuietly(preparedStatement);
            Helpers.closeQuietly(connection);
        }
    }