code: @Override
      public FunctionalTermNullability evaluateNullability(ImmutableList<? extends NonFunctionalTerm> arguments,
                                                           VariableNullability childNullability) {
          // TODO: implement it seriously
          boolean isNullable = arguments.stream()
                  .filter(a -> a instanceof Variable)
                  .anyMatch(a -> childNullability.isPossiblyNullable((Variable) a));
          return new FunctionalTermNullabilityImpl(isNullable);
      }
docs: TODO: REMOVE IT (TEMPORARY)