public synchronized boolean canUndo() {
		return transaction == null && !undoList.isEmpty();
	}
Determine if there is a previous transaction that can be reverted/undone (see {@link #undo()}).

@return true if there is a previous transaction that can be reverted/undone, else false.
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/model/data/StandAloneDataTypeManager.java