TSVIONTodoGet() has bug!

when I use null-transform plugin and print some debug info, I find the TSVIONTodoGet() return a huge member, I consider it maybe has a bug !
The details shows below:

code in null-transform.c:

TSVIO input_vio;
int64_t towrite = 0;
int64_t avail = 0;

towrite = TSVIONTodoGet(input_vio);
TSDebug("null-transform", "\ttoWrite is %" PRId64 "", towrite);

if (towrite > 0) {
/* The amount of data left to read needs to be truncated by

• the amount of data actually in the read buffer.
  */
  avail = TSIOBufferReaderAvail(TSVIOReaderGet(input_vio));
  TSDebug("null-transform", "\tavail is %" PRId64 "", avail);
  #if MDSN_LOG
  if (log) { TSTextLogObjectWrite(log, "handle_transform() with data to write length: %" PRId64 ", IOBufferReader available data length: %" PRId64 "", towrite, avail);}

  #endif

log info:

20110818.13h51m11s handle_transform() with data to write length: 9223372036854775807, IOBufferReader available data length: 1388