public void assignFrom(StructuredFieldValue sfv) {
        clear();
        Iterator<Map.Entry<Field,FieldValue>> otherValues = sfv.iterator();
        while (otherValues.hasNext()) {
            Map.Entry<Field, FieldValue> otherEntry = otherValues.next();
            setFieldValue(otherEntry.getKey(), otherEntry.getValue());
        }
    }
Clears this and assigns from the given {@link StructuredFieldValue}
document/src/main/java/com/yahoo/document/datatypes/Struct.java