output: #fixed code
                                  public synchronized void deleteRepoByName(String repositoryName) {
          Connection connection = null;
          PreparedStatement preparedStatement = null;
          ResultSet resultSet = null;
  
          try {
              connection = this.dbConfig.getConnection();
              preparedStatement = connection.prepareStatement("delete from repo where name=?;");
  
              preparedStatement.setString(1, repositoryName);
  
              preparedStatement.execute();
          }
          catch(SQLException ex) {
              LOGGER.severe(" caught a " + ex.getClass() + "\n with message: " + ex.getMessage());
          }
          finally {
              Helpers.closeQuietly(resultSet);
              Helpers.closeQuietly(preparedStatement);
              Helpers.closeQuietly(connection);
          }
      }
input: #vulnerable code 
                                  public synchronized void deleteRepoByName(String repositoryName) {
          Connection conn = null;
          PreparedStatement stmt = null;
          ResultSet rs = null;
  
          try {
              conn = this.dbConfig.getConnection();
              stmt = conn.prepareStatement("delete from repo where name=?;");
  
              stmt.setString(1, repositoryName);
  
              stmt.execute();
  
              this.cache.remove(repositoryName);
              this.genericCache.remove(this.repoCountCacheKey);
              this.genericCache.remove(this.repoAllRepoCacheKey);
          }
          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