#vulnerable code 
                                public synchronized boolean saveData(String key, String value) {
        String existing = this.getDataByName(key);

        boolean isNew = false;

        Connection conn = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;

        if (existing != null) {
            try {
                conn = this.dbConfig.getConnection();
                stmt = conn.prepareStatement("UPDATE \"data\" SET \"key\" = ?, \"value\" = ? WHERE  \"key\" = ?");

                stmt.setString(1, key);
                stmt.setString(2, value);
                stmt.setString(3, key);

                stmt.execute();
            }
            catch(SQLException ex) {
                LOGGER.severe(" caught a " + ex.getClass() + "\n with message: " + ex.getMessage());
            }
            finally {
                Helpers.closeQuietly(rs);
                Helpers.closeQuietly(stmt);
                Helpers.closeQuietly(conn);
            }
        }
        else {
            isNew = true;
            try {
                conn = this.dbConfig.getConnection();
                stmt = conn.prepareStatement("INSERT INTO data(\"key\",\"value\") VALUES (?,?)");

                stmt.setString(1, key);
                stmt.setString(2, value);

                stmt.execute();
            }
            catch(SQLException ex) {
                LOGGER.severe(" caught a " + ex.getClass() + "\n with message: " + ex.getMessage());
            }
            finally {
                Helpers.closeQuietly(rs);
                Helpers.closeQuietly(stmt);
                Helpers.closeQuietly(conn);
            }
        }

        // Update cache with new value
        if (value != null) {
            this.cache.put(key, value);
        }
        else {
            this.cache.remove(key);
        }

        return isNew;
    } 
                            #location 25 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public synchronized boolean saveData(String key, String value) {
        String existing = this.getDataByName(key);
        boolean isNew = false;

        Connection connection = null;
        PreparedStatement preparedStatement = null;

        try {
            connection = this.dbConfig.getConnection();

            if (existing != null) {
                preparedStatement = connection.prepareStatement("UPDATE \"data\" SET \"key\" = ?, \"value\" = ? WHERE  \"key\" = ?");
                preparedStatement.setString(1, key);
                preparedStatement.setString(2, value);
                preparedStatement.setString(3, key);
            }
            else {
                isNew = true;
                preparedStatement = connection.prepareStatement("INSERT INTO data(\"key\",\"value\") VALUES (?,?)");
                preparedStatement.setString(1, key);
                preparedStatement.setString(2, value);
            }

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

        // Update cache with new value
        if (value != null) {
            this.cache.put(key, value);
        }
        else {
            this.cache.remove(key);
        }

        return isNew;
    }