:sig
DValue* DValue::get_or_create(String s)

:params
s : child key to create or return
return value : pointer to the child node

:see
0_DValue
2_DValue_key
2_DValue_has

:content
Ensures the value is map-shaped and returns the named child. If the key does not exist, an empty child is created. Creating a non-numeric key on a list-shaped value clears list mode.

```cpp
payload.get_or_create("headers")->get_or_create("Content-Type")->set("text/plain");
```