Win32 CreatePen NULL error

#include <windows.h>
#include <stdio.h>
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow)
{
    static TCHAR szAppName[] = TEXT("Random Walk");
    HWND hwnd;
    MSG msg;
    WNDCLASS wndclass;
    wndclass.style = CS_HREDRAW | CS_VREDRAW;
    wndclass.lpfnWndProc = WndProc;
    wndclass.cbClsExtra = 0;
    wndclass.cbWndExtra = 0;
    wndclass.hInstance = hInstance;
    wndclass.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wndclass.hCursor = LoadCursor(NULL, IDC_ARROW);
    wndclass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
    wndclass.lpszMenuName = NULL;
    wndclass.lpszClassName = szAppName;
    if (!RegisterClass(&wndclass))
    {
        MessageBox(NULL, TEXT("Program requires Windows NT !"), szAppName, MB_ICONERROR);
        return 0;
    }
    hwnd = CreateWindow(szAppName, TEXT("Random Walk"),
                        WS_OVERLAPPEDWINDOW,
                        CW_USEDEFAULT, CW_USEDEFAULT,
                        CW_USEDEFAULT, CW_USEDEFAULT,
                        NULL, NULL, hInstance, NULL);
    ShowWindow(hwnd, iCmdShow);
    UpdateWindow(hwnd);
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return msg.wParam;
}
LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    static int cxClient, cyClient;
    HDC hdc;
    HPEN hPen;
    PAINTSTRUCT ps;
    switch (message)
    {
    case WM_SIZE:
        cxClient = LOWORD(lParam);
        cyClient = HIWORD(lParam);
        return 0;

    case WM_PAINT:
        printf("%d\t%d\n", cxClient, cyClient); //Printing the resolution
        hdc = BeginPaint(hwnd, &ps);
        MoveToEx(hdc, 0, cyClient / 2, NULL);
        int count = 0;

        //Plotting 256 lines each of length (cxClient/256) with different color
        for (int i = 0; i < cxClient; i += cxClient / 256)
        {
            if ((hPen = CreatePen(PS_SOLID, 10, RGB(count, 255, 255))) == NULL)
            {
                DWORD lasterror;
                lasterror = GetLastError();
                printf("We got a NULL Value and last error code was %lu\n", lasterror);
                break;
            }
            else
                SelectObject(hdc, hPen);

            count += 1; // For uniform gradient across width
            LineTo(hdc, i, cyClient / 2);
        }
        DeleteObject(hPen);
        EndPaint(hwnd, &ps);
        return 0;

    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }
    return DefWindowProc(hwnd, message, wParam, lParam);
}