@Override
        protected Expression doConvert(Expression exp) {
            if (exp instanceof OutputExpression) {
                return null;
            }
            return exp;
        }
Validates the indexing script changes in all fields in the current and next search model.

@author geirst
config-model/src/main/java/com/yahoo/vespa/model/application/validation/change/search/IndexingScriptChangeValidator.java