Github user cestella commented on the issue:
https://github.com/apache/metron/pull/718
So, the problem with the old way was that it's confusing and just wrong.
Perhaps an example would help here. For the message
```
{
"title" : "otto is great"
}
```
If I wanted to rename title to `better_title`, I'd expect the following to
work:
```
{
"transformation" : "STELLAR"
,"output" : [ "better_title", "title"]
,"config" : {
"better_title" : "title"
,"title" : "null"
}
}
```
At the end of this, I'd expect either `title` to be gone *or* at the very
least, for it to be set to `null` as that is what I directed it to do, but in
actuality, it'll still be `otto is great`. In fact, the output would be:
```
{
"title" : "otto is great",
"better_title" : "otto is great"
}
```
This becomes even MORE insidious if we start doing things like returning
null from Stellar functions.
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