if(datatype->has_subtype == 1){
// This part handles the problem of non-contiguous memory
old_buf = buf;
- buf = xbt_malloc(count*smpi_datatype_size(datatype));
+ buf = count==0 ? NULL : xbt_malloc(count*smpi_datatype_size(datatype));
if (flags & SEND) {
subtype->serialize(old_buf, buf, count, datatype->substruct);
}