public String rankingExpressionFunctionName() {
        String vespaName = vespaName();
        if (vespaName == null) {
            return null;
        }
        return isConstant() ? "constant(" + vespaName + ")" : FUNCTION_PREFIX + modelName + "_" + vespaName;
    }
Retrieve the valid Vespa name of this node if it is a ranking expression function
model-integration/src/main/java/ai/vespa/rankingexpression/importer/operations/IntermediateOperation.java