private void disallowIndexingOfMaps(Context context, SearchCluster cluster, Schema schema, Field field) {
        DataType fieldType = field.getDataType();
        if ((fieldType instanceof MapDataType) && (((SDField) field).doesIndexing())) {
            context.illegal("Field type '" + fieldType.getName() + "' cannot be indexed for search " +
                            "clusters (field '" + field.getName() + "' in definition '" +
                            schema.getName() + "' for cluster '" + cluster.getClusterName() + "').");
        }
    }
This Validator iterates through all search cluster in the given VespaModel to make sure that there are no custom
structs defined in any of its search definitions.

@author Simon Thoresen Hult
config-model/src/main/java/com/yahoo/vespa/model/application/validation/SearchDataTypeValidator.java