public SpanTree removeSpanTree(String name) {
        if (spanTrees == null) {
            return null;
        }
        SpanTree tree = spanTrees.remove(name);
        if (tree != null) {
            tree.setStringFieldValue(null);
        }
        return tree;
    }
Removes the span tree associated with the given name.

@param name the name of the span tree to remove
@return the span tree previously associated with the given name, or null if it did not exist
document/src/main/java/com/yahoo/document/datatypes/StringFieldValue.java