Use conditional access instead of accessing multiple times

If you have code such as following one, the code is difficult to read and not so performant:

```c#
if (a != null && a.b != null && a.b.c != null && a.b.c[0] != null)
{
    return a.b.c[0];
}
```

Instead, it should be refactored to something like:
```c#
var element = a?.b?.c?[0];
if (element != null)
{
    return element;
}
```
