🐛 fix(test_graph.py): add assertion to check if root node is not None

The test_build_params function was failing when the root node was None. This commit adds an assertion to check if the root node is not None before proceeding with the other assertions.

tests/test_graph.py

@@ -238,6 +238,7 @@ def test_build_params(basic_graph):
     root = get_root_node(basic_graph)
     # Root node is a TimeTravelGuideChain
     # which requires an llm and memory
+    assert root is not None
     assert isinstance(root.params, dict)
     assert "llm" in root.params
     assert "memory" in root.params