code: private IAtom getRingAtom(IBond bond) {
          if (bond.getBegin().getFlag(CDKConstants.ISINRING) && !bond.getBegin().getFlag(CDKConstants.ISPLACED)) {
              return bond.getBegin();
          }
          if (bond.getEnd().getFlag(CDKConstants.ISINRING) && !bond.getEnd().getFlag(CDKConstants.ISPLACED)) {
              return bond.getEnd();
          }
          return null;
      }
docs: Get the unplaced ring atom in this bond
  
  @param bond the bond to be search for the unplaced ring atom
  @return the unplaced ring atom in this bond