Nullable value type may be null.

Converting null literal or possible null value to non-nullable type.

Converting null literal or possible null value to non-nullable type.

Possible null reference return.

The variable 'c' is assigned but its value is never used

The variable 'a' is assigned but its value is never used

The variable 'b' is assigned but its value is never used

Possible null reference argument for parameter 'root' in 'void preorder_traversal_i_compact.PreOrder(TreeNode root)'.

Possible null reference argument for parameter 'root' in 'void preorder_traversal_i_compact.PreOrder(TreeNode root)'.

Possible null reference argument for parameter 'root' in 'void preorder_traversal_iii_compact.PreOrder(TreeNode root)'.

Nullable value type may be null.

Converting null literal or possible null value to non-nullable type.

Converting null literal or possible null value to non-nullable type.

Converting null literal or possible null value to non-nullable type.

Converting null literal or possible null value to non-nullable type.

Converting null literal or possible null value to non-nullable type.

Possible null reference argument for parameter 'root' in 'List<int> binary_tree_bfs.LevelOrder(TreeNode root)'.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Possible null reference argument for parameter 'root' in 'void preorder_traversal_i_compact.PreOrder(TreeNode root)'.

Possible null reference argument for parameter 'root' in 'List<int> binary_tree_bfs.LevelOrder(TreeNode root)'.

Nullable value type may be null.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Dereference of a possibly null reference.

Converting null literal or possible null value to non-nullable type.

Dereference of a possibly null reference.

Dereference of a possibly null reference.