the line self.adj$\_$matrix $=[[$None for i in range$($size$)]$ for x in range$($size$)]$ is not properly intializing the adjacency matrix with None for all possible edges and is causing a runtime error. how do i fix it$?$

class WUGraph $($WUGRAPH$)$:

let adj$\_$matrix: Vertex?$[$Vertex$?[$OptWeight$?]]$

# $^$ ADD YOUR FIELDS HERE

def $\_\_$init$\_\_($self$,$ size: nat?$)$:

print$("$Initializing graph with size:"$)$

# Debugging: Print the size

if size is None:

error$("$Size must not be None"$)$

if size $<0$:

error$("$Size must be a non$-$negative integer"$)$

# Initialize the adjacency matrix with None for all possible edges

self.adj$\_$matrix $=[[$None for i in range$($size$)]$ for x in range$($size$)]$

if self.adj$\_$matrix:

print$("$Adjacency matrix initialized successfully with dimensions $\{$size$\}$x$\{$size$\}")$

else:

print$("$Failed to initialize adjacency matrix"$)$

# $^$ YOUR PART GOES HERE