I'm not sure why we alias the object reference `input` to `in` here.  In Java, arguments (which are often object references) are passed by value. This means you can't impact the reference the caller provides for `input`, although you could mutate the object pointed to by the reference by the usual means. So in this sense, in the code below, saying 

```java
if (null == input) {
  input = new ByteArrayInputStream(new byte[] { });
}
```
is safe, because it won't change the reference the caller used to specify `input`.