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
Fix NPE when ReviewInput's message is empty

Bug: Issue 2877
Change-Id: I3d31af8cdcc26c2dc48c316542f55c402fd63832
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
Merge branch 'stable-2.9' into stable-2.10

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

Conflicts:
	gerrit-server/src/main/java/com/google/gerrit/server/change/PostReview.java

Change-Id: Icfde6f0274f0ccc92773fd5a376e8c27099437ac