<｜begin▁of▁sentence｜>### Instruction:
Given a graph with at least one edge, can you implement a custom edge drawer using the AbstractCairoEdgeDrawer in igraph to draw undirected edges according to your requirements and save the output to a PNG file?
### Response:
import igraph as ig

# Assuming you have a graph `g` with at least one edge to draw
g = ig.Graph(edges=[(0, 1)])

class CustomEdgeDrawer(ig.drawing.edge.AbstractCairoEdgeDrawer):
    def draw_undirected_edge(self, edge, src_vertex, dest_vertex):
        # Custom implementation to draw an undirected edge in your desired way
        pass

# Create a Cairo surface to draw on
surface = ig.drawing.cairo.CairoSurface(400, 400)
ctx = ig.drawing.cairo.CairoContext(surface)

# Create a plot object
plot = ig.Plot(surface, bbox=(400, 400), background='white')
plot.add(g)

# Set the custom edge drawer
custom_edge_drawer = CustomEdgeDrawer(ctx)
plot.set_edge_drawer(custom_edge_drawer)

# Draw the graph
plot.redraw()

# Save to a file
surface.write_to_png('custom_edge_graph.png')
<|EOT|>
