A* find closest walkable node

public Node ClosestWalkableNode(Node node) {
        int maxRadius = Mathf.Max (gridSizeX, gridSizeY) / 2;
        for (int i = 1; i < maxRadius; i++) {
            Node n = FindWalkableInRadius (node.gridX, node.gridY, i);
            if (n != null) {
                return n;

            }
        }
        return null;
    }
    Node FindWalkableInRadius(int centreX, int centreY, int radius) {

        for (int i = -radius; i <= radius; i ++) {
            int verticalSearchX = i + centreX;
            int horizontalSearchY = i + centreY;

            // top
            if (InBounds(verticalSearchX, centreY + radius)) {
                Debug.DrawRay (grid [verticalSearchX, centreY + radius].worldPosition, Vector3.up * 2,Color.green,radius);
                if (grid[verticalSearchX, centreY + radius].walkable) {
                    return grid [verticalSearchX, centreY + radius];
                }
            }

            // bottom
            if (InBounds(verticalSearchX, centreY - radius)) {
                if (grid[verticalSearchX, centreY - radius].walkable) {
                    return grid [verticalSearchX, centreY - radius];
                }
            }
            // right
            if (InBounds(centreY + radius, horizontalSearchY)) {
                Debug.DrawRay (grid [centreY + radius, horizontalSearchY].worldPosition, Vector3.up * 2,Color.red,radius);
                if (grid[centreX + radius, horizontalSearchY].walkable) {
                    return grid [centreX + radius, horizontalSearchY];
                }
            }

            // left
            if (InBounds(centreY - radius, horizontalSearchY)) {
                Debug.DrawRay (grid [centreY - radius, horizontalSearchY].worldPosition, Vector3.up * 2,Color.red,radius);
                if (grid[centreX - radius, horizontalSearchY].walkable) {
                    return grid [centreX - radius, horizontalSearchY];
                }
            }

        }

        return null;

    }

    bool InBounds(int x, int y) {
        return x>=0 && x<gridSizeX && y>= 0 && y<gridSizeY;
    }