@Override
    public FieldValue getFieldValue(StructuredFieldValue doc) {
        StringFieldValue sfv = (StringFieldValue) super.getFieldValue(doc);
        Map<String, SpanTree> trees = extractSpanTrees.get(doc);
        if (trees != null) {
            for (SpanTree tree : trees.values()) {
                sfv.setSpanTree(tree);
            }
        }
        return sfv;
    }
This adds an Extractor to the ExtendedField that can be used to get access the backed spantrees
used in the concrete document types.
@author baldersheim
document/src/main/java/com/yahoo/document/ExtendedStringField.java