Here are five possible code completions for the given function signature, addressing the CWE-476 (NULL Pointer Dereference) vulnerability:

1.
```c
{
    if (!line || !lc) {
        return -EINVAL;
    }

    lc->flags |= GPIO_V2_LINE_FLAG_EDGE_DETECTOR;

    if (edflags & GPIOEVENT_REQUEST_RISING_EDGE)
        lc->flags |= GPIO_V2_LINE_FLAG_EDGE_RISING;
    if (edflags & GPIOEVENT_REQUEST_FALLING_EDGE)
        lc->flags |= GPIO_V2_LINE_FLAG_EDGE_FALLING;

    return 0;
}
```

2.
```c
{
    int ret = 0;

    if (!line || !lc) {
        return -EINVAL;
    }

    lc->flags |= GPIO_V2_LINE_FLAG_EDGE_DETECTOR;

    switch (edflags) {
    case GPIOEVENT_REQUEST_RISING_EDGE:
        lc->flags |= GPIO_V2_LINE_FLAG_EDGE_RISING;
        break;
    case GPIOEVENT_REQUEST_FALLING_EDGE:
        lc->flags |= GPIO_V2_LINE_FLAG_EDGE_FALLING;
        break;
    case GPIOEVENT_REQUEST_BOTH_EDGES:
        lc->flags |= GPIO_V2_LINE_FLAG_EDGE_RISING | GPIO_V2_LINE_FLAG_EDGE_FALLING;
        break;
    default:
        ret = -EINVAL;
    }

    return ret;
}
```

3.
```c
{
    if (!line || !lc) {
        return -EINVAL;
    }

    lc->flags |= GPIO_V2_LINE_FLAG_EDGE_DETECTOR;

    if (edflags & GPIOEVENT_REQUEST_RISING_EDGE)
        lc->flags |= GPIO_V2_LINE_FLAG_EDGE_RISING;
    if (edflags & GPIOEVENT_REQUEST_FALLING_EDGE)
        lc->flags |= GPIO_V2_LINE_FLAG_EDGE_FALLING;

    lc->id[line_idx] = line->id;

    return 0;
}
```

4.
```c
{
    if (!line || !lc) {
        return -EINVAL;
    }

    memset(lc, 0, sizeof(*lc));
    lc->flags = GPIO_V2_LINE_FLAG_EDGE_DETECTOR;

    if (edflags & GPIOEVENT_REQUEST_RISING_EDGE)
        lc->flags |= GPIO_V2_LINE_FLAG_EDGE_RISING;
    if (edflags & GPIOEVENT_REQUEST_FALLING_EDGE)
        lc->flags |= GPIO_V2_LINE_FLAG_EDGE_FALLING;

    lc->num_attrs = 1;
    lc->attrs[0].id = line_idx;
    lc->attrs[0].flags = lc->flags;

    return 0;
}
```

5.
```c
{
    if (!line || !lc) {
        return -EINVAL;
    }

    lc->flags |= GPIO_V2_LINE_FLAG_EDGE_DETECTOR;

    if (edflags & GPIOEVENT_REQUEST_RISING_EDGE)
        lc->flags |= GPIO_V2_LINE_FLAG_EDGE_RISING;
    if (edflags & GPIOEVENT_REQUEST_FALLING_EDGE)
        lc->flags |= GPIO_V2_LINE_FLAG_EDGE_FALLING;

    lc->num_attrs = 1;
    lc->attrs[0].mask = BIT(line_idx);
    lc->attrs[0].attr.id = GPIO_V2_LINE_ATTR_ID_FLAGS;
    lc->attrs[0].attr.flags = lc->flags;

    return 0;
}
```

Each of these implementations includes a check for NULL pointers at the beginning to address the CWE-476 vulnerability. They also provide different ways of setting up the edge detector configuration based on the provided flags and line index.