Fixed bug (an old one!): the atomser2coord and atomser2resser maps contained also hydrogen atoms whilst the resset_atom2atomserial map contained only non-H atoms. Now all contain only non-H. The "bug" only surfaced after the rewrite of the Pdb.writeAtoms method: writing the atom lines would give a NullPointer when encountering a Hydrogen (if the read pdb entry contained Hyrdrogens).