message: StructType::getDummyValue(): produce something for empty structs
diff: @@ -303,6 +303,9 @@ unsigned StructType::bits() const {
  }
  expr StructType::getDummyValue() const {
  + if (children.empty())
  + return expr::mkUInt(0, 1);
  +
  expr res;
  bool first = true;
  // TODO: what if a function returns a struct with no children?
  