code: private static StaticAnalysisResult isListExpressionEmpty(ForNode node) {
      Optional<RangeArgs> rangeArgs = RangeArgs.createFromNode(node);
      if (rangeArgs.isPresent()) {
        return isRangeExpressionEmpty(rangeArgs.get());
      }
      ExprNode expr = node.getExpr().getRoot();
      if (expr instanceof ListLiteralNode) {
        return ((ListLiteralNode) expr).numChildren() > 0
            ? StaticAnalysisResult.FALSE
            : StaticAnalysisResult.TRUE;
      }
      return StaticAnalysisResult.UNKNOWN;
    }
docs: consider moving this to SoyTreeUtils or some similar place.