PPPinterface: remove faulty address getter check for invalid pointer

[michalpasztamobica]

Description

Summary of change

(edited after Seppo's remark)
PPPInterface address getter had reversed logic of the check - this is fixed now, by removing the check entirely.

Documentation

Pull request type

[x] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[x] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

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Reviewers

@kivaisan

[ciarmcom]

@michalpasztamobica, thank you for your changes.
@kivaisan @ARMmbed/mbed-os-ipcore @ARMmbed/mbed-os-maintainers please review.

[SeppoTakalo]

API does NOT permit a NULL, therefore you should NOT check for null.

This causes broken code to continue running, when it should have crashed.

[michalpasztamobica]

@SeppoTakalo , I see your point and I now simply removed the faulty check. Please, review again.

[kivaisan]

API does NOT permit a NULL, therefore you should NOT check for null.

Why API was then defined with a pointer parameter? A reference would have been more safe in that case.

[SeppoTakalo]

Yes, reference would be safer, but does not leave any glue that this parameter is going to be modified, also feels more natural for C developers. Therefore using pointers is a dominant in Mbed OS.

[kjbracey]

In my experience, references aren't really much "safer", but they do serve as documentation that null isn't acceptable. It's still quite easy to generate null references that crash in exactly the same way.

They do at least block you from literally doing get_ip_address(nullptr), but no-one's really going to do that. The danger is more from allocation failures or similar. Being a reference parameter isn't going to stop you making a mistake like this:

 SockAddr *addrs = (SockAddr *)malloc(16 * sizeof SockAddr);
 for (int i = 0; i < 16; i++) {
      get_ip_address(i, addr[i]);
  }

(And if something like that did happen, I would rather get_ip_address exploded to help me spot and find the flawed calling code).

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