Add null check for return values of functions that are mostly (but not
always) checked for null.
E.g., since 98% of calls to protocol_stack_interface_info_get_by_id
check for null, it is likely that the function can return null values in
some cases, and omitting the check could crash the program.
9a9085d4cd Updated coap service to be compatible with mbed TLS 3.0 (#135)
git-subtree-dir: connectivity/nanostack/coap-service
git-subtree-split: 9a9085d4cd74ad96320f448a890df43a0cdedbb0
```
connectivity
├── netsocket
├── lwipstack
├── nanostack
│ ├── mbed_lib.json // nanostack-interface's mbed_lib.json
│ ├── include
│ │ └── nanostack // headers from features/netsocket/nanostack-interface
│ ├── source // sources from features/netsocket/nanostack-interface
│ ├── coap-service // used by Thread only - deprecate?
│ ├── mbed-mesh-api
│ ├── nanostack-hal-mbed-cmsis-rtos // HAL porting layer for Nanostack on mbed with CMSIS-RTOS
│ ├── sal-stack-nanostack
│ └── sal-stack-nanostack-eventloop
├── cellular // previously in features/cellular/framework/
├── ...
```
This PR is a part of a wider \connectivity refactoring and implements the above new directory structure for \nanostack.
Mingjie Shen
Arto Kinnunen
Arto Kinnunen
Abbas Bracken Ziad
Ashok Rao