output: #fixed code
                                public void writeTo( Writer writer, WriterConfig config ) throws IOException {
      if( writer == null ) {
        throw new NullPointerException( "writer is null" );
      }
      if( config == null ) {
        throw new NullPointerException( "config is null" );
      }
      WritingBuffer buffer = new WritingBuffer( writer, 128 );
      write( config.createWriter( buffer ) );
      buffer.flush();
    }
input: #vulnerable code 
                                public void writeTo( Writer writer, WriterConfig config ) throws IOException {
      WritingBuffer buffer = new WritingBuffer( writer, 128 );
      write( config == null ? new JsonWriter( buffer ) : config.createWriter( buffer ) );
      buffer.flush();
    } 
                              #location 4 
                              #vulnerability type RESOURCE_LEAK