RFR: JDK-8300245: Replace NULL with nullptr in share/jfr/ [v7]

[Johan Sjölen]

> Hi, this PR changes all occurrences of NULL to nullptr for the subdirectory share/jfr/. Unfortunately the script that does the change isn't perfect, and so we
> need to comb through these manually to make sure nothing has gone wrong. I also review these changes but things slip past my eyes sometimes.
> 
> Here are some typical things to look out for:
> 
>     No changes but copyright header changed (probably because I reverted some changes but forgot the copyright).
>     Macros having their NULL changed to nullptr, these are added to the script when I find them. They should be NULL.
>     nullptr in comments and logs. We try to use lower case "null" in these cases as it reads better. An exception is made when code expressions are in a comment.
> 
> An example of this:
> 
> // This function returns null
> void* ret_null();
> // This function returns true if *x == nullptr
> bool is_nullptr(void** x);
> 
> Note how nullptr participates in a code expression here, we really are talking about the specific value nullptr.
> 
> Thanks!

Johan Sjölen has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 11 commits:

 - Missing fixes
 - Merge branch 'master' into JDK-8300245
 - It's impossible for an array to be nullptr, remove asserts.
   
   Fails build on Clang systems
 - Merge remote-tracking branch 'origin/master' into JDK-8300245
 - Fix outdated copyright
 - Manual fix
 - Fix two faulty NULL_STRING misses
 - More manual fixes
 - Merge remote-tracking branch 'origin/master' into JDK-8300245
 - Manual fixes
 - ... and 1 more: https://git.openjdk.org/jdk/compare/5c7ede94...cb705720

-------------

Changes: https://git.openjdk.org/jdk/pull/12034/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12034&range=06
  Stats: 2070 lines in 125 files changed: 1 ins; 4 del; 2065 mod
  Patch: https://git.openjdk.org/jdk/pull/12034.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/12034/head:pull/12034

PR: https://git.openjdk.org/jdk/pull/12034