beauregard has a really pedantic compiler:

/home/bueler/pism/src/base/util/io/PISMNC4_HDF5.cc: In member function ‘virtual int pism::NC4_HDF5::create_impl(const string&)’:
/home/bueler/pism/src/base/util/io/PISMNC4_HDF5.cc:485:19: warning: converting to non-pointer type ‘MPI_Info {aka int}’ from NULL [-Wconversion-null]
   MPI_Info info = NULL;
                   ^