# Problem in sparse matrix multiplication

I’m trying to use cusparseDcsrgemm2 to do sparse matrix multiplication C=A*B. However, when I call function

cusparseDcsrgemm2_bufferSizeExt(handle, m, n, k, &alpha,
descrA, nnzA, csrRowPtrA, csrColIndA,
descrB, nnzB, csrRowPtrB, csrColIndB,
NULL,
NULL, 0, NULL, NULL,
info,
&bufferSize);

with beta and matrix D as NULL, I got the segmentation fault. If I replace NULL with a random matrix D here, the function is fine. I wonder what I should put here if I do not have matrix D?