Fix NPE when submitting review with inline comments via REST

NPE occurs when submitting a review with inline comments in
the format:

  {
    "comments": {
      "test.txt": [
        {
          "line": 1,
          "message": "comment"
        },
      ]
    }
  }

The comma following the closing brace after the `"message": "comment"`
line seems to be causing an iterator with a null element to be
generated.

NPE does not occur when the comma is omitted.

To prevent the NPE remove the null element from the iterator.

Change-Id: I248739fce955522f7ee4a93441e48914342d3d7d
Fix NPE in /projects/{name}/children?recursive when a parent is missing

If there is a broken edge in the parent graph treat it as having no
children instead of throwing NPE and failing the REST API call.

Change-Id: Ib72f76f04f5804d2b953f0951d3304fc1d6329a2
Gracefully handle `buck audit` failure

Handle exception raised when invoking `buck audit` and exit
with an error message, instead of dumping a python Traceback.

Change-Id: I3786c4eddffa03117f4437314fc12ee68c689a85
Fix NPE when ReviewInput's message is empty

Bug: Issue 2877
Change-Id: I3d31af8cdcc26c2dc48c316542f55c402fd63832
Mention deprecation of sortkey parameters in 2.9 release notes

Bug: Issue 2878
Change-Id: Idd16d5c932b3237cbaeeb8fc8f31e3ebcbf45034
Merge "Gracefully handle `buck audit` failure" into stable-2.9
Make `-S` an alias of `--start` in changes query REST API

The option had been added with the name `-S`.  Change the name
to `--start` with `-S` as an alias, making it consistent with the
naming in other REST APIs.

Add the option to the documentation.

Remove the documentation of `-P` and `-N`. These options only exist
to support online reindexing from clients with outdated JS, and are
deprecated. Keeping them in the documentation will potentially
cause confusion.

Bug: Issue 2878
Change-Id: I992acf4a3d1aeebb1ef40c6fed1afcb0fe26fa92
Add full names for options on list projects REST API

Change-Id: I1dd7a8b2e27b8172cd8f11c9047063070fa6e698
Add full names for options on list groups REST API

Change-Id: I6663eda2adc00c493624438a16ecbf4818e740e1
Merge "Fix NPE when ReviewInput's message is empty" into stable-2.9
Merge "Fix NPE when submitting review with inline comments via REST" into stable-2.9
Merge "Fix NPE in /projects/{name}/children?recursive when a parent is missing" into stable-2.9