public final StringBuilder toString(SerializationContext context) {
        return toString(new StringBuilder(), context, null, null);
    }
Returns the value of evaluating this expression over the given context.

@param context the variable bindings to use for this evaluation
@throws IllegalArgumentException if there are variables which are not bound in the given map
searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/ExpressionNode.java