Based on the provided code slice and the specified vulnerability range (CWE-476, NULL Pointer Dereference), here are five possible patches to address the vulnerability:

Patch 1:
```c
if (str == NULL) {
    SetLastError(ERROR_INVALID_PARAMETER);
    return -1;
}
WINPR_ASSERT(str);
```

Patch 2:
```c
if (!str) {
    return 0;
}
WINPR_ASSERT(str);
```

Patch 3:
```c
WINPR_ASSERT(str != NULL);
if (!str) {
    SetLastError(ERROR_INVALID_PARAMETER);
    return -1;
}
```

Patch 4:
```c
if (str == NULL || len == 0) {
    return 0;
}
WINPR_ASSERT(str);
```

Patch 5:
```c
if (!str) {
    WINPR_ASSERT(FALSE);
    SetLastError(ERROR_INVALID_PARAMETER);
    return -1;
}
```

These patches aim to check for NULL pointers before using the 'str' variable, preventing potential NULL pointer dereferences and improving the overall robustness of the code.