select error with null string -- error code -209

I am using following codes to get the accountname, and account from the
Table Account;
accountname, and account are varchar(30) and it can be null.
The code has no problem when both accountname, and account are not
null.  It gives me an errror code of -209 when the account is null.
Anyone has any idea of fixing it.

the output looks like :
error in fetch -209

Thanks,


  EXEC SQL BEGIN DECLARE SECTION;
  char query_string[256];
  char name[30];
  char account[30];
   EXEC SQL END DECLARE SECTION;



  EXEC SQL CONNECT TO :dbname user :userid/:passwd;
  if(sqlca.sqlcode) {
    printf("error in connect\n");
    return FALSE;
  }
  sprintf(query_string, "SELECT accountname, account FROM Account where
AccountID = %d", customerId);

  EXEC SQL PREPARE sql_command FROM :query_string;
  EXEC SQL DECLARE c_cursor2 CURSOR FOR sql_command;/* DECLARE a cursor
*/
  EXEC SQL OPEN c_cursor2;
  if(sqlca.sqlcode) {
    printf("error in cursor\n");
    return FALSE;
  }
  EXEC SQL FETCH c_cursor2 INTO :name, :account;
  if(sqlca.sqlcode) {
    printf("error in fetch %d\n", sqlca.sqlcode);
    return FALSE;
  }