@Override
    public IfNode setChildren(List<ExpressionNode> children) {
        if (children.size() != 3) throw new IllegalArgumentException("Expected 3 children but got " + children.size());
        return new IfNode(children.get(0), children.get(1), children.get(2));
    }
The average probability that the condition of this node will evaluate to true, or null if not known
searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/IfNode.java