diff --git a/schematic/visualization/tangled_tree.py b/schematic/visualization/tangled_tree.py
index 07757a14d..d5b838e85 100644
--- a/schematic/visualization/tangled_tree.py
+++ b/schematic/visualization/tangled_tree.py
@@ -688,7 +688,7 @@ def get_node_layers_json(self, topological_gen, source_nodes, child_parents, par
 
         return layers_json
 
-    def save_outputs(self, save_file, layers_json, cn='', all_layers=[]):
+    def save_outputs(self, save_file, layers_json, cn='', all_layers=None):
         '''
         Inputs:
             save_file (bool): Indicates whether to save a file locally or not.:
@@ -702,6 +702,8 @@ def save_outputs(self, save_file, layers_json, cn='', all_layers=[]):
                 If save_file == False: Each string represents contains the layers for a single tangled tree.
                 If save_file ==True: is an empty list.
         '''
+        if all_layers is None:
+            all_layers = []
         if save_file == True:
             if cn:
                 output_file_name = f"{self.schema_abbr}_{self.figure_type}_{cn}_tangled_tree.json"
diff --git a/tests/test_api.py b/tests/test_api.py
index 9d69c63b2..6cbb72448 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -881,6 +881,7 @@ def test_visualize_attributes(self, client, data_model_jsonld):
 
     @pytest.mark.parametrize("figure_type", ["component", "dependency"])
     def test_visualize_tangled_tree_layers(self, client, figure_type, data_model_jsonld):
+        # TODO: Determine a 2nd data model to use for this test, test both models sequentially, add checks for content of response
         params = {
             "schema_url": data_model_jsonld,
             "figure_type": figure_type