7adb137409
When you call MPI_Graph_create with a old_comm of size N, and pass nnodes=(N=1), then the Nth proc is supposed to get MPI_COMM_NULL out. The code in this base function didn't properly handle the proc(s) that are supposed to get MPI_COMM_NULL out. cmr=v1.7.5:reviewer=hjelmn This commit was SVN r31145.