private void addExpression(ScriptExpression expression) {
        if ( expression.isEmpty()) return;
        expressions.add(new StatementExpression(new ClearStateExpression(), new GuardExpression(expression)));
    }
An indexing language script derived from a schema. An indexing script contains a set of indexing
statements, organized in a composite structure of indexing code snippets.

@author bratseth
config-model/src/main/java/com/yahoo/schema/derived/IndexingScript.java