Right now the model requires a tree, and we need to be able to work with the model in the context of the model by itself, without any particular tree. We can keep an empty variable for the tree, but we need to make sure we test for the existence of a tree in the contexts when one is required. We also need to make sure we can read and write models without having a tree.
Right now the model requires a tree, and we need to be able to work with the model in the context of the model by itself, without any particular tree. We can keep an empty variable for the tree, but we need to make sure we test for the existence of a tree in the contexts when one is required. We also need to make sure we can read and write models without having a tree.