Assertin failed: unknown bindtype with unknown varlen

Hi,
I get this error "unknown bindtype with unknown varlen" when calling 
dbconvert() in dblib.
This is my situation:
I have table with VARBINARY column with value which is empty not null 
(dbdatlen() = 0)
Then I call dbconvert with srctype=SQLBINARY, srclen=0, 
desttype=SQLBINARY, destlen > 0 and I get above mentioned assertion.

Looking into dbconvert there is in the begining (note condition: srclen==0):

     if (src == NULL || srclen == 0) {
         int bind = dbbindtype(desttype);
         int size = tds_get_size_by_type(desttype);

         if (SYBCHAR == desttype) {
             if (destlen > 0) {
                 size = destlen;
                 bind = CHARBIND;
             } else {
                 size = 1;
                 bind = NTBSTRINGBIND;
             }
         }

         dbgetnull(dbproc, bind, size, dest);   // <--- HERE OCCURS 
ASSERTION
         return size;
     }

Next look into dbgetnull():

     /*
      * For variable-length types, nonpositive varlen indicates
      * buffer is "big enough" but also not to pad.
      * Apply terminator (if applicable) and go home.
      */
     if (varlen <= 0) {
         switch (bindtype) {
         case STRINGBIND:
         case NTBSTRINGBIND:
             varaddr[pnullrep->len] = '\0';
             /* fall thru */
         case CHARBIND:
         case VARYCHARBIND:
+      case BINARYBIND:       // <--- MISSING HERE ?
+      case VARYBINBIND:     // <--- MISSING HERE ?
             break;

As BINARYBIND is not handled ATM default is executed:
         default:
             assert(!"unknown bindtype with unknown varlen");

Can you please fix it ?
Thanks
-Laco.