to_html crashes with ZeroDivisionError on graphs with zero edges

[pedrolbacelar]

Bug

to_html in graphify/export.py crashes with ZeroDivisionError when the graph has nodes but zero edges.

How to reproduce

Build a graph where all semantic edges were filtered out (e.g. malformed extraction) but AST nodes exist. The graph has nodes with degree 0.

from graphify.export import to_html

# Graph with nodes but no edges
G = nx.Graph()
G.add_node("a", label="A")
G.add_node("b", label="B")
communities = {0: ["a", "b"]}
to_html(G, communities, "out.html")  # ZeroDivisionError

Root cause

Line 349:

max_deg = max(degree.values()) if degree else 1

When all nodes have degree 0, max(degree.values()) returns 0 (not falsy), so the if degree else 1 guard doesn't trigger. Then line 358:

size = 10 + 30 * (deg / max_deg)  # division by zero

Suggested fix

max_deg = max(degree.values()) if degree else 1
if max_deg == 0:
    max_deg = 1

I have a PR ready for this: #217 (pending)

[safishamsi]

Fixed in v0.4.2. The degree normalization now uses max(degree.values(), default=1) or 1 to avoid ZeroDivisionError on empty graphs.