Get or create a value from/in an associative array.
Given an associative array to modify and a key,
attempt to retrieve a value from the associative array.
If a value for the given key is not set, set the value in
the associative array to the default value for the value's type.
Get or create a value from/in an associative array.
Given an associative array to modify and a key, attempt to retrieve a value from the associative array. If a value for the given key is not set, set the value in the associative array to the default value for the value's type.
The value will be returned by reference.