diff --git a/tests/test_export.py b/tests/test_export.py
index 77233182..7194d8b7 100644
--- a/tests/test_export.py
+++ b/tests/test_export.py
@@ -639,3 +639,18 @@ def test_to_json_proceeds_on_empty_existing(tmp_path):
     assert to_json(_mkG(3), {}, str(p), force=False) is True
     data = json.loads(p.read_text())
     assert len(data["nodes"]) == 3
+
+
+def test_to_html_handles_null_source_file_and_label(tmp_path):
+    """#1775: a node with source_file=None or label=None must not crash to_html
+    (synthetic/aggregate nodes legitimately carry null source_file; JSON `null`
+    survives .get()'s default). Regression guard — fixed via sanitize_label's
+    None-coercion + the str(source_file or "") call-site guard."""
+    import networkx as nx
+    G = nx.Graph()
+    G.add_node("n1", label="Foo", source_file=None, community=0)
+    G.add_node("n2", label=None, source_file="a.py", community=0)
+    G.add_node("n3", label=None, source_file=None, community=0)
+    out = tmp_path / "graph.html"
+    to_html(G, {0: ["n1", "n2", "n3"]}, str(out))
+    assert out.exists() and out.stat().st_size > 0
diff --git a/tests/test_security.py b/tests/test_security.py
index 2f69be6b..74669f93 100644
--- a/tests/test_security.py
+++ b/tests/test_security.py
@@ -219,6 +219,12 @@ def test_sanitize_label_safe_passthrough():
     assert sanitize_label("MyClass") == "MyClass"
     assert sanitize_label("extract_python") == "extract_python"
 
+def test_sanitize_label_none_returns_empty():
+    # #1775: a node with source_file=None / label=None (synthetic/aggregate
+    # nodes, or JSON `null`) must not raise — .get() returns None, not the
+    # default, when the key is present-but-null.
+    assert sanitize_label(None) == ""
+
 
 # ---------------------------------------------------------------------------
 # check_graph_file_size_cap (#F4 — graph-load memory bomb protection)