code: private static IBond getBond(IAtomContainer container, EdgeToBondMap bondMap, int u, int v) {
          if (bondMap != null) return bondMap.get(u, v);
          return container.getBond(container.getAtom(u), container.getAtom(v));
      }
docs: Obtain the bond between the atoms at index 'u' and 'v'. If the 'bondMap'
  is non-null it is used for direct lookup otherwise the slower linear
  lookup in 'container' is used.
  
  @param container a structure
  @param bondMap   optimised map of atom indices to bond instances
  @param u         an atom index
  @param v         an atom index (connected to u)
  @return the bond between u and v