@Override
    public int hashCode() {
        int result = name.hashCode();
        result = 31 * result + root.hashCode();
        result = 31 * result + annotations.hashCode();
        return result;
    }
Returns the StringFieldValue that this SpanTree belongs to.

@return the StringFieldValue that this SpanTree belongs to, if any, otherwise null.
document/src/main/java/com/yahoo/document/annotation/SpanTree.java