Conditional member access for map children?

Any chance we can add conditional member access for map children?

Example:

Today it works like this  

```
Map coolMap = {
  'foo':'bar'
};

final thing = coolMap['baz']['broke'] // error
```


Tomorrow it works like this?  

```
Map coolMap = {
  'foo':'bar'
};

final thing = coolMap?.['baz']?.['broke'] // null
```