code: @Override
      public KamNode getKamNode(final Kam kam, BelTerm belTerm) {
          if (kam == null) throw new InvalidArgument("missing KAM");
          if (belTerm == null) throw new InvalidArgument("missing BEL term");
          if (!exists(kam)) return null;
          return getKamNode(kam, belTerm.getLabel());
      }
docs: {@inheritDoc}