Fix bug in NetcdfFile.empty where rootgroup gets created twice
Fix bug in NetcdfFile.empty where rootgroup gets created twice

Unidata/netcdf-java,Unidata/netcdf-java,Unidata/netcdf-java,Unidata/netcdf-java,Unidata/netcdf-java,Unidata/netcdf-java,Unidata/netcdf-java