When count= 0, mpich should not raise error if  array_of_requests is NULL.  Otherwise, one has to write code like if (count) MPI_Startall(count, reqs).  Note reqs is often NULL if count=0.  See also MPI_Waitall, which has the correct logic.  

MPI_Startall(int count, MPI_Request array_of_requests[]) {

...

        MPIR_ERRTEST_COUNT(count, mpi_errno);

        MPIR_ERRTEST_ARGNULL(array_of_requests, "array_of_requests", mpi_errno);

}

--Junchao Zhang

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