datawidget.py: raise AttributeError manually if item is graph, was not always raised; maybe problem of #52

src/gui_qt/data/datawidget/datawidget.py

@@ -350,6 +350,9 @@ class DataTree(QtWidgets.QTreeWidget):
             _id = item.data(0, QtCore.Qt.UserRole)
             if _id in ids:
                 try:
+                    if item.parent() is None:
+                        raise AttributeError
+
                     idx = item.parent().indexOfChild(item)
                     item.parent().takeChild(idx)
                     if _id in self._checked_sets: