* return the union of their types. If {@code nodes} is empty or
* {@code null}, returns a new {@link org.yinwang.pysonar.types.UnknownType}.
*/
@NotNull
protected Type resolveUnion(@NotNull Collection<? extends Node> nodes, State s) {
Type result = Type.UNKNOWN;
for (Node node : nodes) {
Type nodeType = transformExpr(node, s);
result = UnionType.union(result, nodeType);
}
return result;
}